Motor control device and electric power steering device

ABSTRACT

A motor control device for driving a brushless motor includes a current detecting unit which detects respective phase currents which flow into the brushless motor; a control calculation unit which calculates instruction values showing respective phase voltages to be applied to the brushless motor, and outputs the instruction values as phase voltage instruction values; a phase resistance calculation unit which calculates respective phase resistance values based on detection values of the respective phase currents detected by the current detecting unit, and the instruction values of the respective phase voltages applied to the brushless motor at the time of the detection of the detection values; a correction unit which corrects the phase voltage instruction values according to the respective phase resistance values calculated by the phase resistance calculation unit; and a driving unit which drives the brushless motor based on the phase voltage instruction values after correction by the correction unit.

The present application is a Divisional application of U.S. patentapplication Ser. No. 12/812,678, filed on May 13, 2011, the entirecontents of which is incorporated herein by reference, which is aNational Stage application of PCT application PCT/JP09/050,510, filed onJan. 16, 2009, which claims priority of Japanese application nos.2008-006658, filed Jan. 16, 2008, 2008-023646, filed Feb. 4, 2008 and2008-030151, filed Feb. 12, 2008.

TECHNICAL FIELD

The present invention relates to a motor control device for driving abrushless motor, and an electric power steering device including such amotor control device.

BACKGROUND ART

An electric power steering device which gives steering assist power to asteering mechanism of a vehicle has conventionally been an electricmotor driven according to the steering torque applied to a handle(steering wheel) by a driver. Although a brush motor has conventionallybeen widely used as an electric motor of an electric power steeringdevice, a brushless motor has recently been also used from viewpoints ofimprovements in reliability and durability, reduction of inertia, or thelike.

In order to control the torque generated in a motor, generally, a motorcontrol device detects an electric current which flows into the motor,and performs PI control (proportional integral control) based on thedifference between an electric current to be supplied to the motor, andthe detected current. In order to detect currents of two or more phases,two or three current sensors are provided in the motor control devicewhich drives a 3-phase brushless motor.

In addition, in connection with the present application invention,obtaining a d-axis voltage instruction value and a q-axis voltageinstruction value using the circuit equation of a motor is disclosed inJP-A-2001-187578. Additionally, correcting a d-axis current instructionvalue according to the temperature of a motor is disclosed inJP-A-2000-184773.

DISCLOSURE OF THE INVENTION Technical Problem

In the motor control device included in the electric power steeringdevice, the current sensor needs to detect a large current of 100 A orhigher. This current sensor is large-sized and hinders miniaturizationof the control device of the electric power steering device. For thisreason, reduction of current sensors becomes a challenge in the motorcontrol device included in the electric power steering device or thelike. If current sensors can be reduced, the costs and power consumptionof the motor control device can also be reduced.

As a method of reducing the current sensors, a method of reducing thecurrent sensors to one and performing the same feedback control as aconventional technique, a method of removing all current sensors, andperforming an open loop control according to the circuit equation of themotor, or the like are considered.

In the former method of these methods, there is a problem in that aplurality of phase currents required for the feedback control may beunable to be detected by one current sensor depending on the rotationalposition of the rotor of the motor, and control of the motor may becomediscontinuous. On the other hand, such a problem does not occur in thelatter method. However, in the latter method, unlike the feedbackcontrol concerning an electric current, there is a problem in that aripple (referred to as a “torque ripple”) is generated in the outputtorque of the motor when a difference is caused in resistance betweenphases due to the following factors.

i) As relays are arranged in two phases for fail-safe, resistancedifference equivalent to the contact resistances of the relays iscaused.

ii) The contact resistances of connectors for connecting the motor withthe motor control device are different from each other between phases.

Particularly, in the electric power steering device, the smoothness ofthe output torque of the motor is be treated as important from theviewpoint of an improvement in steering feel. Thus, suppressinggeneration of such a torque ripple is required.

Additionally, the brushless motor for steering assist is driven by amotor drive circuit built in an electronic control unit (hereinafterreferred to as “ECU”). In the electric power steering device, sinceminiaturization, high efficiency, and low cost are demanded, variousproposals are made as to integration or the like of this ECU and thebrushless motor.

Meanwhile, when there is a difference between phases as to resistancecomponents in a motor/driving circuit system including a brushless motorand a driving circuit, generation of the ripple (referred to as a“torque ripple”) in the output torque of the motor becomes a problem.Particularly, in the electric power steering device, the smoothness ofthe output torque of the motor is to be treated as important from theviewpoint of an improvement in steering feel. Thus, suppressinggeneration of such a torque ripple is required.

On the other hand, in the electric power steering device, there issuggested a configuration (for example, refer to JP-A-2005-319971) whichincludes a resistance adjusting means which adjusts the resistancecomponents in the motor/driving circuit system so that the interphasedifference (hereinafter referred to as an “interphase resistancedifference”) between the resistance components in the motor/drivingcircuit system including a brushless motor and a driving circuit isequal to or less than a predetermined value.

However, when a resistance is applied in order to eliminate theinterphase resistance difference in the motor/driving circuit system,degradation of the efficiency in driving or response of the brushlessmotor is caused. For this reason, in a circuit board (hereinafterreferred to as a “motor driving circuit board”) on which the drivingcircuit of the motor is mounted, it is preferable to form a wiringpattern so that the interphase resistance difference in themotor/driving circuit system is eliminated.

However, when an attempt to form a wiring pattern so that the torqueripple is sufficiently reduced is made, the circuit pattern in the abovemotor driving circuit board becomes complicated, and the space forforming the circuit pattern increases. That is, in the motor drivingcircuit board, it is possible to design the wiring pattern so thatwiring resistances of paths from a power supply terminal to a groundingterminal are aligned between phases. However, it is difficult to makethe wiring resistances sufficiently small to such a degree that does notinfluence motor driving, or to symmetrically arrange the switchingelements which constitute the motor drive circuit. For this reason, whenthe wiring pattern is formed so that a resistance component (hereinafterreferred to as an “upper stage arm resistance”) from the power supplyterminal to the output end of the motor drive circuit and a resistancecomponent (hereinafter referred to as a “lower stage arm resistance”)from the output end to the grounding terminal are aligned, the circuitpattern becomes complicated, a large space for forming the circuitpattern becomes necessary, and the size of the board increases. As aresult, in the electric power steering device, the board area within theECU becomes large, and this runs counter to the above demand forminiaturization or the like.

Therefore, an object of the invention is to provide a motor controldevice which can drive a brushless motor so that generation of a torqueripple resulting from generation of the interphase resistance differenceis suppressed. Additionally, another object of the invention is toprovide an electric power steering device including such a motor controldevice.

Still another object of the invention is to provide a motor controldevice which can reduce a torque ripple while suppressing an increase inthe size of a circuit board on which a driving circuit of a brushlessmotor is mounted. Additionally, a still further object of the inventionis to provide an electric power steering device including such a motorcontrol device.

Technical Solution

In a first invention, a motor control device for driving a brushlessmotor, the motor control device includes: a control calculation meanswhich obtains a phase voltage instruction value showing a phase voltageto be applied to the brushless motor; a current detecting means whichdetects an electric current which flows into the brushless motor; arotational position detecting means which detects the rotationalposition of a rotor in the brushless motor; a correction means whichcorrects the phase voltage instruction value based on the detectionresult of the current detecting means and the detection result of therotational position detecting means so that a dependency of a ratio onan electric angle shown by a secondary harmonic component of the ratioconcerning the electric angle of the brushless motor, the ratio being aratio of a q-axis or d-axis component of the electric current, whichflows into the brushless motor, to a q-axis or d-axis instruction value;and a driving means which drives the brushless motor based on the phasevoltage instruction value after the correction by the correction means.

In a second invention, according to the first invention, the controlcalculation means calculates q-axis and d-axis components of a voltageto be applied to the brushless motor as q-axis and d-axis voltageinstruction values, respectively, and converts the q-axis and d-axisvoltage instruction values into phase components of the voltage to beapplied to the brushless motor, thereby obtaining the phase voltageinstruction value, and the correction means includes: a data acquisitionmeans which calculates at least one of the ratio of the q-axis componentof the electric current which flows into the brushless motor to a q-axisvoltage instruction value, and the ratio of the d-axis component of theelectric current which flows into the brushless motor to a d-axisvoltage instruction value, based on the detection result of the currentdetecting means, and correlates the calculated ratio with the electricangle of the brushless motor based on the detection result of therotational position detecting means so as to be stored asangle-dependent data; a correction coefficient determination means whichdetermines a correction coefficient for correcting the phase voltageinstruction value, based on the angle-dependent data, so that thedependency on the electric angle shown by the secondary harmoniccomponent is reduced; and a correction execution means which correctsthe phase voltage instruction value based on the correction coefficientdetermined by the correction coefficient determination means.

In a third invention, according to the first invention, the controlcalculation means determines q-axis and d-axis components of an electriccurrent to flow to the brushless motor as q-axis and d-axis currentinstruction values, respectively, calculates the q-axis and d-axiscomponents of the voltage to be applied to the brushless motors asq-axis and d-axis voltage instruction values, respectively, based on theq-axis and d-axis current instruction values, and converts the q-axisand d-axis voltage instruction values into phase components,respectively, of the voltage to be applied to the brushless motor,thereby obtaining the phase voltage instruction value, and thecorrection means includes: a data acquisition means which calculates atleast one of the ratio of the q-axis component of the electric currentwhich flows into the brushless motor to the q-axis current instructionvalue, and the ratio of the d-axis component of the electric currentwhich flows into the brushless motor to the d-axis current instructionvalue, based on the detection result of the current detecting means, andcorrelates the calculated ratio with the electric angle of the brushlessmotor based on the detection result of the rotational position detectingmeans so as to be stored as angle-dependent data; a correctioncoefficient determination means which determines a correctioncoefficient for correcting the phase voltage instruction value, based onthe angle-dependent data, so that the dependency on the electric angleshown by the secondary harmonic component is reduced; and a correctionexecution means which corrects the phase voltage instruction value basedon the correction coefficient determined by the correction coefficientdetermination means.

In a fourth invention, according to the first invention, the correctionmeans corrects the phase voltage instruction value so that thedependency on the electric angle shown by the secondary harmoniccomponent is reduced, based on the detection values of the electriccurrent and rotational position obtained by the current detecting meansand the rotational position detecting means when the detection value ofthe electric current obtained by the current detecting means is smallerthan a predetermined threshold value.

In a fifth invention, according to the first invention, the correctionmeans corrects the phase voltage instruction value so that thedependency on the electric angle shown by the secondary harmoniccomponent is reduced, based on the detection values of the electriccurrent and rotational position obtained by the current detecting meansand the rotational position detecting means when the angular velocity ofthe rotor of the brushless motor is equal to or lower than apredetermined threshold value.

In a sixth invention, an electric power steering device gives steeringassist power to a steering mechanism of a vehicle by a brushless motor,and the electric power steering device includes: the motor controldevice according to any one of first to fifth inventions, wherein themotor control device drives the brushless motor which gives steeringassist power to the steering mechanism.

According to the above first invention, the phase voltage instructionvalue is corrected so that the dependency of the q-axis or d-axiscomponent of the electric current (motor current) which flows into thebrushless motor on the electric angle is reduced. Thereby, thedifference caused between phases as to the motor current by thedifference (interphase resistance difference) of the resistance valuesbetween phases is reduced or eliminated, and the torque ripple generatedin the brushless motor due to the interphase resistance difference issuppressed.

According to the above second invention, at least one of the ratio ofthe q-axis component of the electric current (motor current) which flowsinto the brushless motor to a q-axis voltage instruction value, and theratio of the d-axis component of the motor current to a d-axis voltageinstruction value is calculated, and the calculated ratio is correlatedwith the electric angle so as to be acquired as angle-dependent data.Since this angle-dependent data is data based on the ratio of the motorcurrent to the voltage instruction value, the influence on the q-axis ord-axis component of the motor current caused by a change in an appliedvoltage to the brushless motor is removed, and the dependency of theq-axis or d-axis component of the motor current on the electric angle isappropriately shown. The phase voltage instruction value is corrected sothat the dependency of the q-axis or d-axis component of the electriccurrent which flows into the brushless motor on the electric angle isreduced based on such angle-dependent data. Accordingly, the torqueripple generated in the brushless motor due to the interphase resistancedifference can be more reliably suppressed.

According to the above third invention, at least one of the ratio of theq-axis component of the electric current (motor current) which flowsinto the brushless motor to a q-axis current instruction value, and theratio of the d-axis component of the motor current to a d-axis currentinstruction value is calculated, and the calculated ratio is correlatedwith the electric angle so as to be acquired as angle-dependent data.Since this angle-dependent data is data based on the ratio of the motorcurrent to the current instruction value, the influence on the q-axis ord-axis component of the motor current caused by a change (or a change inthe applied voltage corresponding thereto) in an electric current to besupplied to the brushless motor, i.e., a change in the currentinstruction value, is removed, and the dependency of the q-axis ord-axis component of the motor current on the electric angle isappropriately shown. The phase voltage instruction value is corrected sothat the dependency of the q-axis or d-axis component of the electriccurrent which flows into the brushless motor on the electric angle isreduced based on such angle-dependent data. Accordingly, the torqueripple generated in the brushless motor due to the interphase resistancedifference can be more reliably suppressed.

According to the above fourth invention, the detection value of themotor current and the detection value of the rotational position of therotor of the motor which are used to correct the phase voltageinstruction value are acquired when the detection value of the motorcurrent is smaller than a predetermined threshold value. That is, sincethe motor current is smaller than the threshold value, the currentdetection value and rotational position detection value for correctionare acquired when an increase in the resistance value caused bygeneration of heat is small. Thereby, since the current detection valueand rotational position detection value, which are acquired when theinterphase resistance difference is relatively large compared to theresistance value, are used for correction of the phase voltageinstruction value, the correction of compensating the interphaseresistance difference with high precision becomes possible, andgeneration of the torque ripple resulting from the interphase resistancedifference can be more reliably suppressed.

According to the fifth invention, the detection value of the motorcurrent and the detection value of the rotational position of the rotorof the motor which are used to correct the phase voltage instructionvalue are acquired when the angular velocity of the rotor of thebrushless motor is equal to or less than a predetermined thresholdvalue. That is, the current detection value and the rotational positiondetection value are acquired when a counter-electromotive force issmall, and applied voltages to respective phase resistances arecomparatively large. By using such current detection value androtational position detection value, the correction for compensating theinterphase resistance difference with high precision becomes possible,and generation of the torque ripple resulting from the interphaseresistance difference can be more reliably suppressed.

According to the above sixth invention, since generation of the torqueripple resulting from the interphase resistance difference is suppressedby correcting the phase voltage instruction value showing a voltage tobe applied to the brushless motor which gives steering assist power, anelectric power steering device with a favorable steering feel can beprovided.

In a seventh invention, a motor control device for driving a brushlessmotor, the motor control device includes: a current detecting meanswhich detects respective phase currents which flow into the brushlessmotor; a control calculation means which calculates instruction valuesshowing respective phase voltages to be applied to the brushless motor,and outputs the instruction values as phase voltage instruction values;a phase resistance calculation means which calculates respective phaseresistance values based on detection values of the respective phasecurrents detected by the current detecting means, and the instructionvalues of the respective phase voltages applied to the brushless motorat the time of the detection of the detection values; a correction meanswhich corrects the phase voltage instruction values according to therespective phase resistance values calculated by the phase resistancecalculation means; and a driving means which drives the brushless motorbased on the phase voltage instruction values after correction by thecorrection means.

In a eighth invention, according to the seventh invention, the phaseresistance calculation means calculates respective phase resistancevalues when the magnitude of the current which flows into the brushlessmotor is smaller than a predetermined value.

In a ninth invention, according to the seventh invention, a storagemeans which stores the phase voltage instruction values after thecorrection when the respective phase currents are detected by thecurrent detecting means is further included, wherein the phaseresistance calculation means calculates the respective phase resistancevalues based on the detection values of the respective phase currentsdetected by the current detecting means, and the phase voltageinstruction values stored in the storage means.

In a tenth invention, according to the ninth invention, the currentdetecting means includes: a single current sensor which detects theelectric current which flows through into the brushless motor; and aphase current calculation means which calculates the detection values ofthe respective phase currents sequentially, based on the detection valueof the electric current detected by the current sensor, the controlcalculation means includes: an open-loop-control means which calculatesthe phase voltage instruction values according to the circuit equationof the brushless motor based on an instruction value showing an electriccurrent to be supplied to the brushless motor, and the angular velocityof the rotor of the brushless motor; and a parameter calculation meanswhich calculates the values of the parameters used when the phasevoltage instruction values are calculated according to the circuitequation, based on the detection value of the electric current detectedby the current sensor, and the storage means stores the phase voltageinstruction values after correction whenever the detection value of anyphase current is obtained by the phase current calculation means.

In a eleventh invention, an electric power steering device givessteering assist power to a steering mechanism of a vehicle by abrushless motor, and the electric power steering device includes: themotor control device according to any one of the seventh to tenthinventions, wherein the motor control device drives the brushless motorwhich gives steering assist power to the steering mechanism.

According to the above seventh invention, respective phase resistancevalues are calculated based on detection values of the respective phasecurrents detected by the current detecting means, and the instructionvalues of the respective phase voltages obtained by the controlcalculation means, and the instruction values of the respective phasevoltages to be applied to the brushless motor are corrected according tothe calculated respective phase resistance values, whereby theinterphase resistance difference is compensated, and the torque rippleresulting from the interphase resistance difference is reduced.

According to the above eighth invention, when the magnitude of anelectric current which flows into the brushless motor is smaller than apredetermined value, respective phase resistances are calculated, and atthe time of this calculation, an increase in resistance value resultingfrom generation of heat caused by an electric current is small and theinterphase resistance difference is relatively large. Thus,high-precision calculation values are acquired as to respectiveresistances. Thereby, since compensation of the interphase resistancedifferences by correction of the instruction values of the respectivephase voltages is more accurately performed, the torque ripple can besufficiently reduced.

According to the above ninth invention, the instruction values of therespective phase voltages applied to the brushless motor at the time ofthe detection of the respective phase currents are stored in the storagemeans, and the respective phase resistance values are calculated basedon the detection values of the respective phase currents, and theinstruction values of the respective phase voltages stored in thestorage means. Accordingly, even in a case where electric currents ofall phases cannot be detected since the number of a current sensor isonly one, and respective phase current detection values are sequentiallyobtained based on the current detection value obtained by the currentsensor, the torque ripple can be reduced by calculating respective phaseresistance values, and correcting the instruction values of therespective phase voltages according to the respective phase resistancevalues.

According to the above tenth invention, the values of the parameters tobe used when the instruction values of the respective phase voltages areobtained, are obtained on the basis on the detection value of theelectric current detected by the single current sensor, and theinstruction values of the respective phase voltages are correctedaccording to the respective phase resistance values calculated based onthe detection values of the respective phase currents sequentiallyobtained by the current detecting means including a single currentsensor, and the instruction values of the respective phase voltagesstored in the storage means. Thereby, while the costs or consumedelectric current are suppressed compared to a case where a plurality ofcurrent sensors are used, the brushless motor can be driven with highprecision even when the values of the above parameters fluctuate due tomanufacturing variations, temperature change, or the like, and motoroutput with a suppressed torque ripple can be obtained.

According to the above eleventh invention, since generation of thetorque ripple resulting from the interphase resistance difference issuppressed by correcting the instruction values of the respective phasevoltages showing a voltage to be applied to the brushless motor whichgives steering assist power, an electric power steering device with afavorable steering feel can be provided.

In a twelfth invention, a motor control device for driving a brushlessmotor, includes: a control calculation means which obtains instructionvalues showing respective phase voltages to be applied to the brushlessmotor, and outputs the instruction values as phase voltage instructionvalues; a correction means which corrects the phase voltage instructionvalues; and a driving means which drives the brushless motor based onthe phase voltage instruction values after correction by the correctionmeans, wherein the driving means is adapted such that switching elementpairs including two switching elements mutually connected in series areconnected in parallel between a power supply terminal and a groundingterminal by the number of phases, and includes an inverter in which aconnection point between the two switching elements corresponding toeach phase is connected to the brushless motor as an output end, andwherein the correction means corrects the phase voltage instructionvalues for every phase according to the phase voltage instruction valuesso that the deviation of a voltage at the output end caused by thedifference between a resistance component of a path from the powersupply terminal to the output end of the inverter and a resistancecomponent of a path from the output end to the grounding terminal iscompensated.

In a thirteenth invention, according to the twelfth invention, thecorrection means includes: a storage means which stores a correction mapshowing the correspondence relationship between the instruction valuesof phase voltages to be applied to the brushless motor, and the amountsof correction for every phase; and a correction operation means whichcorrects the phase voltage instruction values for every phase accordingto the amounts of correction correlated with the phase voltageinstruction values output from the control calculation means by thecorrection map, thereby calculating the phase voltage instruction valuesafter correction.

In a fourteenth invention, an electric power steering device givessteering assist power to a steering mechanism of a vehicle by abrushless motor, and the electric power steering device includes: themotor control device according to the twelfth or thirteenth invention,wherein the motor control device drives the brushless motor which givessteering assist power to the steering mechanism.

According to the above twelfth invention, the phase voltage instructionvalues are corrected for every phase according to the phase voltageinstruction values showing voltages to be applied to the brushlessmotor. Thereby, even in a case where there is a difference in the upperstage arm resistance which is a resistance component of the path fromthe power supply terminal to the output end of the inverter, and thelower stage arm resistance which is a resistance component of the pathfrom the output end to the grounding terminal, the phase voltagesaccording to the phase voltage instruction values are applied to thebrushless motor with high precision. This suppresses generation of thetorque ripple resulting from the difference between the upper stage armresistance and the lower stage arm resistance in the inverter.Additionally, the phase voltage instruction values showing voltages tobe applied to the brushless motor are corrected for every phase so thatthe voltage deviation at the output end of the inverter is compensated.Thus, even in a case where the interphase resistance difference exists,the interphase imbalance between phase voltages applied to the brushlessmotor is suppressed. Thereby, generation of the torque ripple resultingfrom the interphase resistance difference can also be reduced.Accordingly, when a circuit pattern is formed so that the resistancecomponents are aligned between the upper stage arm and lower stage armof the inverter or between phases in order to reduce the torque ripple,an increase in the size of the circuit board of the inverter is caused.However, according to the above first invention, the torque ripple canbe reduced to suppress an increase in the size of the circuit board bycorrecting the phase voltage instruction values as described above.

According to the above thirteenth invention, a correction map showingthe correspondence relationship between the instruction values of phasevoltages to be applied to the brushless motor, and the amounts ofcorrection is prepared for every phase. Thus, the same effects as thoseof the above first invention are obtained by correcting the phasevoltage instruction values for every phase based on the correction map.In addition, such a correction map can be made by computer simulationregarding a system including a brushless motor and a motor controldevice, or simple calculation based on an equivalent circuit for onephase regarding a motor/driving circuit system. That is, the voltagedeviation (or relationship between the duty ratio of the inverter, andvoltage deviation) at the output end of each phase of the inverter canbe obtained by the computer simulation or the simple calculation basedon the equivalent circuit, using design values or actual measurements ofthe upper stage arm resistance and lower stage arm resistance for eachphase of the inverter, or the phase resistance of the brushless motor,and the correction map can be made based on the voltage deviation or thelike.

According to the above fourth invention, since the torque ripple can bereduced while suppressing an increase in the size of the circuit boardof the inverter for driving the brushless motor, steering feel can beimproved while meeting the demand for miniaturization, high efficiency,or the like in the electric power steering device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of an electric powersteering device related to an embodiment of the invention.

FIG. 2 is a block diagram showing the configuration of a motor controldevice related to a first embodiment of the invention.

FIG. 3 is a view showing a 3-phase alternating-current coordinate and adq coordinate in a 3-phase brushless motor.

FIG. 4 is a view for explaining the principle of correction of a phasevoltage instruction value in the above first embodiment.

FIG. 5( a) is a graph showing the q-axis gain value when R_(v)>R_(w) orR_(u).

FIG. 5( b) is a graph showing the q-axis gain value when R_(u)>R_(v) orR_(v).

FIG. 5( c) is a graph showing the q-axis gain value when R_(w)>R_(u) orR_(v).

FIG. 6( a) is a graph showing the q-axis gain value where the peakelectrical angle θp is 150 degrees.

FIG. 6( b) is a graph showing the q-axis gain value where the peakelectrical angle θp is 165 degrees.

FIG. 6( c) is a graph showing the q-axis gain value where the peakelectrical angle θp is 180 degrees.

FIG. 6( d) is a graph showing the q-axis gain value where the peakelectrical angle θp is 195 degrees.

FIG. 7( a) is a graph showing the q-axis gain value when R_(v)>R_(w) orR_(u) in another embodiment.

FIG. 7( b) is a graph showing the q-axis gain value when R_(u)>R_(v) orR_(v) in another embodiment.

FIG. 7( c) is a graph showing the q-axis gain value when R_(w)>R_(u) orR_(v) in another embodiment.

FIG. 8 is a block diagram showing the configuration of a motor controldevice related to a second embodiment of the invention.

FIG. 9 is a block diagram showing the configuration of a motor controldevice related to a third embodiment of the invention.

FIG. 10 is a view for explaining a calculation method of phaseresistance in the above third embodiment.

FIG. 11 is a flow chart for explaining an example of the operation of aphase resistance calculating unit in the above third embodiment.

FIG. 12 is a block diagram showing the configuration of a motor controldevice related to a fourth embodiment of the invention.

FIG. 13 is a block diagram showing the configuration of a motor controldevice related to a fifth embodiment of the invention.

FIG. 14 is a view for explaining the making of a correction map in theabove embodiment.

FIG. 15( a) is a circuit diagram showing an equivalent circuit for onephase for obtaining voltage deviation required for the making of thecorrection map in the above embodiment, where the x-phase flows into thebrushless motor.

FIG. 15( b) is a circuit diagram showing an equivalent circuit for onephase for obtaining voltage deviation required for the making of thecorrection map in the above embodiment, where the x-phase flows from thebrushless motor.

FIG. 16 is a view for explaining a correction map made based on theequivalent circuit shown in FIGS. 15( a) and 15(b).

BEST MODE FOR CARRYING OUT THE INVENTION 1. Electric Power SteeringDevice

FIG. 1 is a schematic diagram showing the configuration of an electricpower steering device related to an embodiment of the invention, alongwith the configuration of a vehicle associated therewith. The electricpower steering device shown in FIG. 1 is a column assist type electricpower steering device including a brushless motor 1, a reducer 2, atorque sensor 3, a vehicle speed sensor 4, a position detecting sensor5, and an electronic control unit (hereinafter referred to as ECU) 10.

As shown in FIG. 1, a handle (steering wheel) 101 is secured to one endof a steering shaft 102, and the other end of the steering shaft 102 isconnected to a rack shaft 104 via a rack-and-pinion mechanism 103. Bothends of the rack shaft 104 are connected to wheels 106 via connectingmembers 105 including a tie rod and a knuckle arm. When a driver rotatesthe handle 101, the steering shaft 102 rotates, and the rack shaft 104reciprocates with this rotation. The direction of the wheels 106 changeswith the reciprocating motion of the rack shaft 104.

The electric power steering device performs steering assist shown below,in order to alleviate a burden to a driver. The torque sensor 3 detectssteering torque T applied to the steering shaft 102 through theoperation of the handle 101. The vehicle speed sensor 4 detects vehiclespeed S. The position detecting sensor 5 detects the rotational positionP of a rotor of the brushless motor 1. The position detecting sensor 5is constituted by, for example, a resolver.

The ECU 10 receives supply of electric power from a vehicle-mountedbattery 100, and drives the brushless motor 1 based on the steeringtorque T, the vehicle speed S, and the rotational position P. When thebrushless motor 1 is driven by the ECU 10, steering assist power isgenerated. The reducer 2 is provided between the brushless motor 1 andthe steering shaft 102. The steering assist power generated by thebrushless motor 1 acts so as to rotate the steering shaft 102 via thereducer 2.

As a result, the steering shaft 102 is rotated by both the steeringtorque applied to the handle 101, and the steering assist powergenerated in the brushless motor 1. In this way, the electric powersteering device gives the steering assist power generated by thebrushless motor 1 to a steering mechanism of the vehicle, therebyperforming steering assist.

The electric power steering device related to the embodiment of theinvention has the feature in a control device (motor control device)which drives the brushless motor 1. Thus, the motor control deviceincluded in the electric power steering device related to respectiveembodiments will be described below.

2. Second Embodiment

FIG. 2 is a block diagram showing the configuration of the motor controldevice related to the first embodiment of the invention. The motorcontrol device shown in FIG. 2 is configured using the ECU 10, anddrives the brushless motor 1 which has windings (not shown) of threephases including u-phase, v-phase, and w-phase. The ECU 10 includes aphase compensator 11, a microcomputer (hereinafter abbreviated as amicrocomputer) 20, a 3-phase/PWM (Pulse Width Modulation) modulator 12,a motor drive circuit 13, and a current sensor 14.

The steering torque T output from the torque sensor 3, the vehicle speedS output from the vehicle speed sensor 4, and the rotational position Poutput from the position detecting sensor 5 are input to the ECU 10. Thephase compensator 11 performs phase compensation on the steering torqueT. The microcomputer 20 functions as a control means which calculates avoltage instruction value used for the driving of the brushless motor 1.The functions of the microcomputer 20 will be described below in detail.

The 3-phase/PWM modulator 12, and the motor drive circuit 13 areconstituted by hardware (circuits), and function as a motor drivingmeans which drives the brushless motor 1, using the voltage of thevoltage instruction value obtained by the microcomputer 20. The3-phase/PWM modulator 12 creates three kinds of PWM signals (U, V, and Wshown in FIG. 2) which have duty ratios according to 3-phase voltageinstruction values obtained by the microcomputer 20. The motor drivecircuit 13 is a PWM voltage type inverter circuit including six MOS-FETs(Metal Oxide Semiconductor Field Effect Transistor) as switchingelements. The six MOS-FETs are controlled by three kinds of PWM signalsand negative signals thereof. By controlling the conduction state of theMOS-FETs using the PWM signals, 3-phase driving currents (a u-phasecurrent, a v-phase current, and a w-phase current) are supplied to thebrushless motor 1.

The current sensor 14 functions as a current detecting means whichdetects an electric current which flows into the brushless motor 1. Thecurrent sensor 14 is constituted by, for example, a resistor and a Halldevice, and only one current sensor is provided between the motor drivecircuit 13 and a power source. In the example shown in FIG. 2, thecurrent sensor 14 is provided between the motor drive circuit 13 and theminus side (grounding) of a power source. However, the current sensor 14may be provided between the motor drive circuit 13 and the plus side ofthe power source.

While the brushless motor 1 is rotating, a current value detected by thecurrent sensor 14 changes according to a PWM signal. Within one cycle ofa PWM signal, a one-phase driving current may be detected by the currentsensor 14, and the sum of two-phase driving currents may be detected bythe current sensor. Since the sum of 3-phase driving currents becomeszero, the remaining one-phase driving current can be obtained based onthe sum of the two-phase driving currents. Accordingly, while thebrushless motor 1 is rotating, 3-phase driving currents can be detectedusing one current sensor 14. A current value i_(a) detected by thecurrent sensor 14 is input to the microcomputer 20.

The microcomputer 20 executes programs stored in a memory (not shown)built in the ECU 10, thereby functioning as an instruction currentcalculating unit 21, an open-loop control unit 22, a dq-axis/3-phaseconversion unit 23, an angle calculating unit 24, an angular velocitycalculating unit 25, a Φ calculating unit 26, a data acquisition unit41, a correction coefficient determining unit 42, and a correctionexecuting unit 43. In addition, the instruction current calculating unit21, the open-loop control unit 22, and the dq-axis/3-phase conversionunit 23 constitute a control calculation means which calculates a phasevoltage instruction value used in order to drive the brushless motor 1.

The microcomputer 20, as shown below, obtains voltage instruction valuesshowing voltages to be given to the motor drive circuit 13, according tocircuit equations of the motor, based on current instruction valuesshowing the number of electric currents to be supplied to the brushlessmotor 1, and the angular velocity of the rotor of the brushless motor 1.

The angle calculating unit 24 obtains the rotational angle (hereinafterreferred to an angle θ) of the rotor of the brushless motor 1 based onthe rotational position P detected by the position detecting sensor 5.The angular velocity calculating unit 25 obtains the angular velocityω_(e) of the rotor of the brushless motor 1 based on the angle θ. Inaddition, when a u-axis, a v-axis, and a w-axis are set for thebrushless motor 1 as shown in FIG. 3, and a d-axis and a q-axis are setfor the rotor 6 of the brushless motor 1, the angle formed by the u-axisand the d-axis becomes the angle θ. That is, in the angle calculatingunit 24, an electric angle θ in the brushless motor 1 is obtained.

The instruction current calculating unit 21 obtains the d-axis componentand q-axis component (hereinafter, the former value is referred to as ad-axis current instruction value i_(d)* and the latter value is referredto as a q-axis current instruction value i_(q)*) of an electric currentto be supplied to the brushless motor 1 based on the steering torque T(an output signal of the phase compensator 11) and the vehicle speed Safter phase compensation. In more detail, the instruction currentcalculating unit 21 has built therein a table (hereinafter referred toas an assist map) which stores the correspondence between the steeringtorque T and instruction currents, with the vehicle speed S as aparameter, and obtains a current instruction value with reference to theassist map. By using the assist map, when a certain magnitude ofsteering torque has been given, it is possible to obtain the d-axiscurrent instruction value i_(d)* and q-axis current instruction valuei_(q)* showing an electric current to be supplied to the brushless motor1 in order to generate an appropriate magnitude of steering assist poweraccording to the magnitude.

In addition, the q-axis current instruction value i_(q)* obtained by theinstruction current calculating unit 21 is a current value with a sign,and the sign shows the direction of the steering assist. For example,when the sign is plus, the steering assist for right turning isperformed, and when the sign is minus, the steering assist for leftturning is performed. Additionally, the d-axis current instruction valuei_(d)* is typically set to zero.

The open-loop control unit 22 obtains the d-axis component and q-axiscomponent (hereinafter the former value is referred to as a d-axisvoltage instruction value v_(d) and the latter value is referred to as aq-axis voltage instruction value v_(q)) of a voltage to be applied tothe brushless motor 1 based on the d-axis current instruction valuei_(d)*, the q-axis current instruction value i_(q)*, and the angularvelocity ω_(e). The d-axis voltage instruction value v_(d) and theq-axis voltage instruction value v_(q) are calculated using circuitequations of a motor shown in the following Equations (1) and (2).

v _(d)=(R+PL _(d))i _(d)*−ω_(e) L _(q) i _(q)*  (1)

v _(q)=(R+PL _(q))i _(q)*+ω_(e) L _(d) i _(d)*+ω_(e)Φ  (2)

Here, in Equations (1) and (2), v_(d) is the d-axis voltage instructionvalue, v_(q) is the q-axis voltage instruction value, i_(d)* is thed-axis current instruction value, i_(q)* is the q-axis currentinstruction value, ω_(e) is the angular velocity of the rotor, R is acircuit resistance including an armature winding resistance, L_(d) isthe self-inductance of the d-axis, L_(q) is the self-inductance of theq-axis, Φ is a √( 3/2) multiple of a maximum value of the number of U,V, and W-phase armature winding interlinking magnetic fluxes, and P is adifferential operator. Among these, R, L_(d), L_(q), and Φ are treatedas known parameters. In addition, the wiring resistance between thebrushless motor 1 and the ECU 10, the resistance and wiring resistanceof the motor drive circuit 13 within the ECU 10, or the like areincluded in the circuit resistance shown by R. This point is also thesame in the other embodiments.

The dq-axis/3-phase conversion unit 23 converts the d-axis voltageinstruction value v_(d) and the q-axis voltage instruction value v_(q)which are calculated by the open-loop control unit 22 into voltageinstruction values on 3-phase alternating-current coordinate axes. Inmore detail, the dq-axis/3-phase conversion unit 23 obtains a u-phasevoltage instruction value V_(u), a v-phase voltage instruction valueV_(v), and a w-phase voltage instruction value V_(w), using thefollowing Equations (3) to (5) based on the d-axis voltage instructionvalue v_(d) and the q-axis voltage instruction value v_(q).

V _(u)=√(⅔)×{v _(d)×cos θ−v _(q)×sin θ}  (3)

V _(v)=√(⅔)×{v _(d)×cos(θ−2π/3)−v _(q)×sin(θ−2π/3)}  (4)

V _(w) =−V _(u) −V _(v)  (5)

The angle θ included in the above Equations (3) and (4) is an electricangle obtained in the angle calculating unit 24. In addition, theu-phase voltage instruction value V_(u), the v-phase voltage instructionvalue V_(v), and the w-phase voltage instruction value V_(w) aregenerically called “phase voltage instruction values V_(u), V_(v), andV_(w).”

The current value i_(a) detected by the current sensor 14, and theelectric angle θ calculated by the angle calculating unit 24, and theq-axis voltage instruction value v_(q) calculated by the open-loopcontrol unit 22 are input to the data acquisition unit 41. The dataacquisition unit 41 first obtains u-phase and v-phase currents(hereinafter, the former value is referred to as a u-phase currentdetection value i_(u) and the latter value is referred to as a v-phasecurrent detection value i_(v)) which flow into the brushless motor 1based on the current value i_(a), and converts these currents intocurrent values on dq coordinate axes. In more detail, the dataacquisition unit 41 obtains the q-axis current detection value i_(q),using the following Equation (6) based on the u-phase current detectionvalue and the v-phase current detection value i_(v).

i _(q)=√2×{i _(v)×cos θ−i _(u)×cos(θ−2π/3)}  (6)

Next, the data acquisition unit 41 obtains the ratio i_(q)/v_(q) of theabove q-axis current detection value i_(q) to the q-axis voltageinstruction value v_(q) (hereinafter referred to as a “relative voltageq-axis current gain value” or a “q-axis current gain value”) whenv_(q)≠0, and stores this q-axis current gain value i_(q)/v_(q) in thedata acquisition unit 41 so as to correspond to the electric angle θcalculated by the angle calculating unit 24 at the time of currentdetection in the current sensor 14. In this way, whenever the q-axiscurrent gain value i_(q)/v_(q) is calculated, the data acquisition unit41 stores the q-axis current gain value i_(q)/v_(q) so as to correspondto the electric angle at this time. Thereby, data (hereinafter referredto as “angle-dependent data”) showing the q-axis current gain valuei_(q)/v_(q) to various electric angles θ of 0 to 360 degrees is obtainedin the data acquisition unit 41. In addition, as will be describedlater, since the dependency of the q-axis current on the electric angleθ is based on a secondary harmonic component, the range of the electricangle θ when the angle-dependent data is acquired may be a rangenarrower than 0 to 360 degrees, for example, a range of 90 to 270degrees (this point is also the same in the modifications and otherembodiments which will be described later).

The correction coefficient determining unit 42 determines correctioncoefficients g_(u), g_(v), and g_(w) for correcting the phase voltageinstruction values V_(u), V_(v), and V_(w), respectively, as will bedescribed later, in the correction executing unit 43, based on theangle-dependent data obtained as described above.

The above correction coefficients g_(u), g_(v), g_(w), and the armaturewinding interlinking magnetic flux number Φ calculated by the Φcalculating unit 26, and the angular velocity ω_(e) calculated by theangular velocity calculating unit 25 are input to the correctionexecuting unit 43, and the correction executing unit 43 corrects thephase voltage instruction values V_(u), V_(v), and V_(w) according tothe following Equations (7) to (9).

V _(uc)=(V _(u) −e _(u))·g _(u) +e _(u)  (7)

V _(vc)=(V _(v) −e _(v))·g _(v) +e _(v)  (8)

V _(wc)=(V _(w) −e _(w))·g _(w) +e _(w)  (9)

In the above Equations (7) to (9), e_(u), e_(v), and e_(w) arerespectively u-phase, v-phase, and w-phase counter-electromotive forces(induced voltages) in the brushless motor 1. Meanwhile, the q-axiscomponent of a counter-electromotive force of the brushless motor 1 isω_(e)Φ, and the d-axis component is 0. Thus, the correction executingunit 43 converts the d-axis components and q-axis components of thesecounter-electromotive forces into counter-electromotive forces on the3-phase alternating-current coordinate axes by the following Equations(10) to (12), and calculates the phase voltage instruction value V_(uc),V_(vc), and V_(wc) after correction, according to the above Equation (7)to (9), using the respective phase counter-electromotive forces e_(u),e_(v) and e_(w) acquired by the conversion.

e _(u)=√(⅔)×{0×cos θ−ω_(e)Φ×sin θ}  (10)

e _(v)=√(⅔)×{0×cos(θ−2π/3)−ω_(e)Φ×sin(θ−2π/3)}  (11)

e _(w) =−e _(u) −e _(v)  (12)

In addition, the angle θ included in the above equations (10) and (11)is an electric angle obtained by the angle calculating unit 24.

In this way, the microcomputer 20 performs the processing of obtainingthe current instruction values i_(d)* and i_(q)* on the dq coordinateaxes, the processing of obtaining the voltage instruction values v_(d)and v_(q) on the dq coordinate axes according to the circuit equationsof the motor, the processing of converting the d-axis and q-axis voltageinstruction values v_(d) and v_(q) into the phase voltage instructionvalues V_(u), V_(v), and V_(w), and the processing of correcting thephase voltage instruction values V_(u), V_(v), and V_(w). The3-phase/PWM modulator 12 outputs three kinds of PWM signals based on thephase voltage instruction values V_(uc) V_(vc), and V_(wc) aftercorrection which have been obtained by the microcomputer 20. Thereby, asinusoidal current according to the respective phase voltage instructionvalues V_(uc), V_(vc), and V_(wc) after correction flows into the3-phase windings of the brushless motor 1, and the rotor of thebrushless motor 1 rotates. Along with this rotation, the torqueaccording to the current which flows through the brushless motor 1 isgenerated in a rotary shaft of the brushless motor 1. The generatedtorque is used for the steering assist.

The current value i_(a) detected by the current sensor 14, and theelectric angle θ calculated by the angle calculating unit 24, and theangular velocity ω_(e) calculated by the angular velocity calculatingunit 25 are input to the Φ calculating unit 26. The Φ calculating unit26 first obtains u-phase and v-phase currents (hereinafter, the formervalue is referred to as a u-phase current detection value i_(u) and thelatter value is referred to as a v-phase current detection value i_(v))which flow into the brushless motor 1 based on the current value i_(a),and converts these currents into current values on the dq coordinateaxes, using the following Equation (13) and (14), thereby obtaining thed-axis current detection value i_(d) and the q-axis current detectionvalue i_(q).

I _(d)=√2×{i _(v)×sin θ−i _(u)×sin(θ−2π/3)}  (13)

i _(q)=√2×{i _(v)×cos θ−i _(u)×cos(θ−2π/3)}  (14)

Next, the Φ calculating unit 26 obtains the armature windinginterlinking magnetic flux number Φ included in Equation (2), using thefollowing Equation (15) based on the q-axis voltage instruction valuev_(q), the d-axis current detection value i_(d), the q-axis currentdetection value i_(q), and the angular velocity ω_(e) when ω_(e)≠0.

Φ={v _(q)−(R+PL _(q))i _(q)−ω_(e) L _(d) i _(d)}/ω_(e)  (15)

In addition, Equation (15) assigns the d-axis current detection valuei_(d) and the q-axis current detection value i_(q) to the d-axis currentinstruction value i_(d)* and q-axis current instruction value i_(q)* ofEquation (2), and solves the Equation for Φ.

The Φ calculating unit 26 outputs the calculated Φ value to theopen-loop control unit 22. The open-loop control unit 22 uses the Φvalue calculated by the Φ calculating unit 26, when the q-axis voltageinstruction value v_(q) is obtained using Equation (2). In this way, themicrocomputer 20 obtains the armature winding interlinking magnetic fluxnumber Φ included in the circuit equations of the motor, and uses the Φvalue when the q-axis voltage instruction value v_(q) is obtained.

The Φ calculating unit 26 may calculate the Φ value with arbitrarytiming, as long as ω_(e)≠0. The Φ calculating unit 26, for example, mayobtain the Φ value at predetermined intervals, may obtain the Φ valueonce after the start of driving of the brushless motor 1, or may obtainthe Φ value when the state of temperature or the like has changed.Additionally, when ω_(e) is close to zero, an error is apt to occur inthe obtained Φ value. Thus, the Φ calculating unit 26 may obtain the Φvalue only when the ω_(e) is equal to or more than a predeterminedthreshold value.

As shown above, the motor control device related to this embodimentobtains the voltage instruction values by the open loop control rotoraccording to the circuit equation, based on the current instructionvalue and the angular velocity of the of the motor, obtains the Φincluded in the circuit equations of the motor based on the currentvalues detected by the current sensor, and uses the Φ value when thevoltage instruction values are obtained. Accordingly, according to themotor control device related to this embodiment, even when the Φ valueincluded in the circuit equations of the motor fluctuates due tomanufacturing variations or a temperature change, the brushless motorcan be driven with high precision to obtain a desired motor output byobtaining the Φ value based on the current values detected by thecurrent sensor.

Additionally, the motor control device related to this embodiment isprovided with only one current sensor. Therefore, according to the motorcontrol device related to this embodiment, miniaturization, low cost,and low power consumption of the motor control device can be achieved byreducing current sensors. Moreover, since the motor control devicerelated to this embodiment performs the open loop control, control ofthe motor does not become discontinuous unlike a motor control devicewhich performs feedback control using one current sensor. Therefore,according to the motor control device related to this embodiment, soundor vibration can be suppressed.

<2.1 Principle of Correction>

In this embodiment, in order to correct the phase voltage instructionvalues V_(u), V_(v), and V_(w) so as to suppress generation of a torqueripple resulting from a difference (hereinafter, this difference isreferred to as an “interphase resistance difference”) between u-phase,v-phase, and w-phase regarding the value of a circuit resistanceincluding an armature winding resistance, a correction unit 40 isprovided. The correction unit 40 is constituted by the data acquisitionunit 41, the correction coefficient determining unit 42, and thecorrection executing unit 43 as stated earlier, and the correctionexecuting unit 43 corrects the phase voltage instruction values V_(u),V_(v), and V_(w), using the correction coefficients g_(u), g_(v), andg_(w) obtained by the data acquisition unit 41 and the correctioncoefficient determining unit 42, according to Equations (7) to (9) asmentioned earlier. Hereinafter, correction of such phase voltageinstruction values V_(u), V_(v), and V_(w) will be described withreference to FIGS. 4 to 6.

FIG. 4 is a view for explaining this principle of correction, and showsthe relationship between the q-axis current which is the q-axiscomponent of an electric current which flow into the brushless motor 1,and the electric angle θ. In more detail, the relationship between aq-axis current i_(qo) and the electric angle θ in a case where there isno interphase resistance difference, and the relationship between aq-axis current i_(qa) and the electric angle θ in a case where there isan interphase resistance difference are shown. Now, circuit resistancesincluding armature winding resistances regarding u-phase, v-phase, andw-phase are referred to as a “u-phase resistance”, a “v-phaseresistance”, and a “w-phase resistance”, respectively, (or collectivelyand generically referred to as a “phase resistance”), and are shown bysymbols “R_(u)”, “R_(v)”, and “R_(w)”, respectively. Additionally, thevalues of the u-phase resistance, the v-phase resistance, and thew-phase resistance are shown by symbols “R_(u)”, “R_(v)”, and “R_(w)”,respectively.

As shown in FIG. 4, the q-axis current i_(qo) in a case where there isno resistance difference between the phase resistances R_(u), R_(v), andR_(w) (R_(u)=R_(v)=R_(w)), that is, in a case where there is nointerphase resistance difference becomes a constant value (fixed)regardless of the electric angle θ. On the other hand, the q-axiscurrent i_(qa) in a case where there is an interphase resistancedifference depends on the electric angle θ. In more detail, the q-axiscurrent i_(qa) in a case where there is an interphase resistancedifference, as shown in FIG. 4, includes a secondary harmonic componentregarding the electric angle θ. This is because, even if the amplitudesof (sinusoidal) u, v and w-phase voltages (sine wave shape) to beapplied to the brushless motor 1 are the same, since the amplitudesbetween the u, v, and w-phase currents i_(u), i_(v), and i_(w) whichflow into the brushless motor 1 are different in a case where there isan interphase resistance difference, the q-axis current i_(q) acquiredfrom Equation (6) is not fixed to a constant value but includes asecondary harmonic component regarding the electric angle θ. Theamplitude and phase angle of this secondary harmonic component differaccording to the magnitude relationship of resistance values between thephase resistances R_(u), R_(v), and R_(w).

Accordingly, by correcting the phase voltage instruction values V_(u),V_(v), and V_(w) according to the phase angle of the q-axis currenti_(q) in the brushless motor 1, the dependency of the q-axis currenti_(q) on the electric angle can be reduced or eliminated, and therebygeneration of a torque ripple resulting from the interphase resistancedifference can be suppressed. The correction unit 40 in this embodimentcorrects the phase voltage instruction values V_(u), V_(v), and V_(w) inorder to suppress the torque ripple based on such a principle.Hereinafter, this correction method will be described in detail.

<2.2 Correction Method>

In this embodiment, as mentioned earlier, the data acquisition unit 41of the correction unit 40 obtains the q-axis current gain valuei_(q)/v_(q) which is the ratio of the q-axis current detection valuei_(q) to the q-axis voltage instruction value v_(q), regarding variouselectric angles θ, and the data showing the q-axis current gain valuei_(q)/v_(q) to various electric angles θ of 0 to 360 degrees is storedas the angle-dependent data in the data acquisition unit 41. Here, thedata showing not the q-axis current detection value i_(q) but the q-axiscurrent gain value i_(q)/v_(q) is stored in order to remove theinfluence on the q-axis current caused by a change in the voltageapplied to the brushless motor 1, thereby appropriately acquiring thedata showing the dependency of the q-axis current to the electric angleθ.

In the correction coefficient determining unit 42 of the correction unit40, an electric angle (hereinafter referred to as a “peak electricangle”) θp at which the q-axis current gain value i_(q)/v_(q) becomesthe greatest is obtained based on the angle-dependent data acquired asdescribed above, and the correction coefficients g_(u), g_(v), and g_(w)in Equations (7) to (9) as mentioned earlier are determined according tothe peak electric angle θp. In addition, although two peaks exist in asecondary harmonic component regarding the electric angle θ included inthe q-axis current gain value i_(q)/v_(q) within a range of θ=0 to 360degrees, the peak electric angle θp included within a range of θ=90 to270 degrees is used for the determination of the correction coefficientsg_(u), g_(v), and g_(w) in this embodiment. Here, the range of theelectric angle θ used for the determination of the correctioncoefficients g_(u), g_(v), and g_(w) is not limited thereto.Additionally, as can be understood from Equations (7) to (9) asmentioned earlier, when the value of the correction coefficient g_(x)(x=u, v, and w) is 1, (the amplitude of) an applied voltage to theresistance R_(x) of a relevant phase is the same as that beforecorrection, and when the value of the correction coefficient g_(x) (x=u,v, and w) is greater than 1, (the amplitude of) an applied voltage tothe resistance R_(x) of a relevant phase becomes greater than thatbefore correction.

Additionally, the following matters are derived from the above Equation(6). That is, when the phase resistances R_(u), R_(v), and R_(w) havethe relationship of R_(v)>R_(w) or R_(u), the peak electric angle θpexists within a range of θ=90 to 150 degrees, for example, as shown inFIG. 5( a), and when the phase resistances have the relationship ofR_(u)>R_(v) or R_(w), the peak electric angle θp exists within a rangeof θ=150 to 210 degrees, for example, as shown in FIG. 5( b), and whenthe phase resistances have the relationship of R_(w)>R_(u) or R_(v), thepeak electric angle θp exists within a range of θ=210 to 270 degrees,for example, as shown in FIG. 5( c).

Thus, in the correction coefficient determining unit 42 in thisembodiment, the correction coefficients g_(u), g_(v), and g_(w) aredetermined as follows. In addition, in the following, when thedetermination of the correction coefficients g_(u), g_(v), and g_(w)based on the angle-dependent data is not made at all, an initial valuewhich is suitable as these correction coefficients g_(u), g_(v), andg_(w), for example, “1” (a value which corresponds to no correction) isset.

(A1) In the Case of 90 [deg]≦θp<150 [deg]

The value obtained by increasing a v-phase correction coefficient g, atthis time is newly set to a v-phase correction coefficient g_(v). Thismeans that an applied voltage to the v-phase resistance R_(v) is madegreater than that before correction in order to reduce the amplitudedifference between the v-phase current and the u-phase and w-phasecurrents.

(A2) In the Case of 150 [deg]≦θp<210 [deg]

The value obtained by increasing a u-phase correction coefficient g_(u)at this time is newly set to a u-phase correction coefficient g_(u).This means that an applied voltage to the u-phase resistance R_(u) ismade greater than that before correction in order to reduce theamplitude difference between the u-phase current and the v-phase andw-phase currents.

(A3) In the Case of 210 [deg]≦θp<270 [deg]

The value obtained by increasing a w-phase correction coefficient g_(w)at this time is newly set to a w-phase correction coefficient g_(w).This means that an applied voltage to the w-phase resistance R_(w) ismade greater than that before correction in order to reduce theamplitude difference between the w-phase current and the u-phase andv-phase currents.

According to the corrections like the above (A1) to (A3), the amplitudedifference between u-phase, v-phase, and w-phase currents is reduced oreliminated. Thus, the dependency of the q-axis current i_(q) on theelectric angle θ is eliminated, and as a result, the torque ripple inthe brushless motor 1 is suppressed. Hereinafter, specific examples ofsuch corrections will be further described.

For example, in a case where the peak electric angle θp obtained basedon the above angle-dependent data is 150 [deg] as shown in FIG. 6( a),the phase resistances R_(u), R_(v), and R_(w) have the relationship ofR_(u)=R_(v)>R_(w). In this case, in the correction coefficientdetermining unit 42, the u-phase and v-phase correction coefficientsg_(u) and g_(v) at this time are changed to, for example, the values of1.1 multiples thereof. Additionally, in a case where the peak electricangle θp obtained based on the above angle-dependent data is 165 [deg]as shown in FIG. 6( b), the phase resistances R_(u), R_(v), and R_(w)have the relationship of R_(u)>R_(v)>R_(w). In this case, in thecorrection coefficient determining unit 42, the u-phase correctioncoefficient g_(u) at this time is changed to, for example, the value of1.1 multiples thereof, and the v-phase correction coefficient g, at thistime is changed to, for example, the value of 1.05 multiples thereof.Moreover, in a case where the peak electric angle θp obtained based onthe above angle-dependent data is 180 [deg] as shown in FIG. 6( c), thephase resistances R_(u), R_(v), and R_(w) have the relationship ofR_(u)>R_(v)=R_(w). In this case, in the correction coefficientdetermining unit 42, the u-phase correction coefficient g_(u) at thistime is changed to, for example, the value of 1.1 multiples thereof.Furthermore, in a case where the peak electric angle θp obtained basedon the above angle-dependent data is 195 [deg] as shown in FIG. 6( d),the phase resistances R_(u), R_(v), and R_(w) have the relationship ofR_(u)>R_(w)>R_(v). Therefore, in the correction coefficient determiningunit 42, the u-phase correction coefficient g_(u) at this time ischanged to, for example, the value of 1.1 multiples thereof, and thew-phase correction coefficient g_(w) at this time is changed to, forexample, the value of 1.05 multiples thereof.

In the above description, the multiplying factor when the correctioncoefficients g_(u), g_(v), and g_(w) at this time is changed, or thevalue after the change is determined according to the fluctuation range(amplitude) of the secondary harmonic component regarding the electricangle θ included in the q-axis current gain value i_(q)/v_(q). Inaddition, numeric values including “1.1 multiples” or “1.05 multiples”shown above are merely examples. Practically, it is preferable to adjustthe method of determining the correction coefficients g_(u), g_(v), andg_(w) by the correction coefficient determining unit 42 so thatappropriate correction coefficients g_(u), g_(v), and g_(w) aredetermined using experimental data or computer simulation results thatthe dependency of the q-axis current on the electric angle θ issuppressed.

In the correction executing unit 43, the phase voltage instructionvalues V_(u), V_(v), and V_(w) are corrected according to the aboveEquations (7) to (9), using the correction coefficient g_(u), g_(v), andg_(w) determined as described above. Such phase voltage instructionvalues V_(uc), V_(vc), and V_(wc) after correction are used for drivingof the brushless motor 1 as mentioned earlier.

As described above, related to this embodiment, the phase voltageinstruction values are corrected so that the dependency of the q-axiscurrent on the electric angle θ that the secondary harmonic componentconcerning the electric angle θ of the q-axis current shows is reducedor eliminated. Thus, the interphase resistance difference is compensatedto suppress generation of a torque ripple resulting from the interphaseresistance difference. Accordingly, a favorable steering feel can beprovided to a driver by using the motor control device related to thisembodiment in order to drive the brushless motor 1 which generates thesteering assist power in the electric power steering device as shown inFIG. 1.

3. Modification of First Embodiment

Next, a modification of the above embodiment will be described. Inaddition, among constituent elements of the modification as will bedescribed below, the same constituent elements as those of the aboveembodiment, or constituent elements corresponding thereto will be shownby the same reference numerals, and the detailed descriptions thereofare omitted.

In the above embodiment, the data showing the q-axis current gain valuei_(q)/v_(q) to various electric angles θ of 0 to 360 degrees is acquiredas the angle-dependent data by the data acquisition unit 41, and thecorrection coefficients g_(u), g_(v), and g_(w) are determined by thecorrection coefficient determining unit 42 based on this angle-dependentdata. Instead of this, however, the data showing the d-axis current gainvalue i_(d)/v_(d) to various electric angles θ of 0 to 360 degrees(relative voltage) may be acquired as the angle-dependent data by thedata acquisition unit 41, and the correction coefficients g_(u), g_(v),and g_(w) may be determined through the correction coefficientdetermining unit 42 based on this angle-dependent data. According tothis configuration, through the correction of the phase voltageinstruction values V_(u), V_(v), and V_(w) using the correctioncoefficients g_(u), g_(v), and g_(w), the dependency of the d-axiscurrent i_(d) on the electric angle θ is reduced or eliminated, and theamplitude difference between the u-phase, v-phase, and w-phase currentsis reduced or eliminated. Thus, the torque ripple in the brushless motor1 can be suppressed similarly to the above embodiment.

Additionally, in the above embodiment, not the data showing the q-axiscurrent detection value i_(q) itself but the data showing the q-axiscurrent gain value i_(q)/v_(q) is acquired as the angle-dependent data.Instead of this, however, the data showing the ratio (hereinafterreferred to as a “relative instruction q-axis current gain value” or a“q-axis current gain value”) i_(q)/i_(q)* of the q-axis currentdetection value i_(q) to the q-axis current instruction value i_(q)* maybe acquired as the angle-dependent data when i_(q)*≠0. The q-axiscurrent instruction value i_(q)* required for acquisition of thisangle-dependent data is obtained from the instruction currentcalculating unit 21. Even by such a modification, it is possible toremove the influence on the q-axis current caused by a change in anelectric current to be supplied to the brushless motor 1, i.e., a changein a current instruction value (or a change in an applied voltage to thebrushless motor 1 corresponding thereto), thereby appropriatelyacquiring the data showing the dependency of the q-axis current on theelectric angle θ. Hereinafter, this modification will be described withreference to FIG. 7.

When the electric angle at which the above q-axis current gain valuei_(q)/i_(q)* becomes the greatest is referred to as a “peak electricangle”, the following matters are derived from Equation (6) as mentionedearlier similarly to the above first embodiment. That is, when the phaseresistances R_(u), R_(v), and R_(w) have the relationship of R_(v)>R_(w)or R_(u), the peak electric angle θp exists within a range of θ=90 to150 degrees as shown in FIG. 7( a), and when the phase resistances havethe relationship of R_(u)>R_(v) or R_(w), the peak electric angle θpexists within a range of θ=150 to 210 degrees as shown in FIG. 7( b),and when the phase resistances have the relationship of R_(w)>R_(u) orR_(v), the peak electric angle θp exists within a range of θ=210 to 270degrees as shown in FIG. 7( c).

Thus, even in this modification, in the correction coefficientdetermining unit 42, the correction coefficients g_(u), g_(v), and g_(w)are determined similarly to the above first embodiment. That is, in thecase of 90 [deg]≦θp<150 [deg], the value obtained by increasing thev-phase correction coefficient g_(v) at this time is newly set to av-phase correction coefficient g_(v). Additionally, in the case of 150[deg]≦θp<210 [deg], the value obtained by increasing the u-phasecorrection coefficient g_(u) at this time is newly set to a u-phasecorrection coefficient g_(u). Moreover, in the case of 210 [deg]≦θp<270[deg], the value obtained by increasing the w-phase correctioncoefficient g_(w) at this time is newly set to a w-phase correctioncoefficient g_(w). The correction executing unit 43 of this modificationalso corrects the phase voltage instruction values V_(u), V_(v), and Vwaccording to Equations (7) to (9) as mentioned earlier, using such newcorrection coefficients g_(u), g_(v), and g_(w).

In addition, the multiplying factor when the correction coefficientsg_(u), g_(v), and g_(w) at this time are changed, or the value after thechange is determined according to the fluctuation range (amplitude) ofthe secondary harmonic component regarding the electric angle θ includedin the q-axis current gain value i_(q)/i_(q)*. Practically, it ispreferable to adjust the method of determining the correctioncoefficients g_(u), g_(v), and g_(w) by the correction coefficientdetermining unit 42 so that appropriate correction coefficients g_(u),g_(v), and g_(w) are determined using experimental data or computersimulation results such that the dependency of the q-axis current on theelectric angle θ is suppressed. Other configurations in thismodification are the same as those of the above embodiment.

Even by the above modification, the amplitude difference betweenu-phase, v-phase, and w-phase currents is reduced or eliminated. Thus,the dependency of the q-axis current i_(q) on the electric angle θ iseliminated, and as a result, the torque ripple in the brushless motor 1is suppressed.

In addition, in the above embodiment or the modification thereof, thetiming with which the data acquisition unit 41 acquires the current gainvalue i_(q)/v_(q), i_(d)/v_(d), or i_(q)/i_(q)* which constitutes theabove angle-dependent data in the above embodiment or modification, thetiming with which the correction coefficient determining unit 42determines new correction coefficients g_(u), g_(v), and g_(w) based onthe above angle-dependent data, and outputs the new correctioncoefficients to the correction executing unit 43 is not particularlylimited. Such acquisition timings of the current gain values or suchoutput timing of the correction coefficients may be set, for example atpredetermined intervals, or when the state of the temperature or thelike has changed, the above angle-dependent data may be acquired so asto output the new correction coefficients g_(u), g_(v), and g_(w).

In addition, in a case where the current gain value i_(q)/v_(q) whichconstitutes the above angle-dependent data is acquired, the timing ofthe data acquisition is not particularly limited if the timing isv_(q)≠0. However, in a case where the q-axis voltage instruction valuev_(q) is close to zero, an error is apt to occur, and the detectionprecision of the peak electric angle θp is reduced. Thus, the currentgain value i_(q)/v_(q) may be acquired so long as the q-axis voltageinstruction value v_(q) is equal to or more than a predetermined lowerlimit. For the same reason, in a case where the current gain valuei_(q)/v_(q)* which constitutes the above angle-dependent data isacquired, and in a case where the q-axis current instruction valuei_(q)* is close to zero, an error is apt to occur, and the detectionprecision of the peak electric angle θp is reduced. Thus, the currentgain value i_(q)/v_(q)* may be acquired so long as the q-axis currentinstruction value i_(q)* is equal to or more than a predetermined lowerlimit (threshold value). Additionally, when the angular velocity ω_(e)of the rotor is large, the counter-electromotive force becomes large,and an applied voltage to respective phase resistances R_(u), R_(v), andR_(w) becomes small. Thus, for this same reason, when the aboveangle-dependent data is acquired, an error is apt to occur, and thedetection precision of the peak electric angle θp is reduced.Accordingly, the above angle-dependent data may be acquired so long asthe angular velocity ω_(e) is equal to or less than a predeterminedupper limit (threshold value). Additionally, since thecounter-electromotive force becomes large when the angular velocityω_(e) is large, the torque ripple becomes small even if there is aninterphase resistance difference. Accordingly, the phase voltageinstruction values V_(u), V_(v), and V_(w) may be corrected in thecorrection executing unit 43 so long as the angular velocity ω_(e) isequal to or less than a predetermined upper limit (refer to Equations(7) to (9)).

Meanwhile, when an electric current (motor current) which flows into thebrushless motor 1 becomes large, the resistance becomes large due togeneration of heat, whereas the interphase resistance difference is notgenerally changed by the currents. Accordingly, when the motor currentbecomes large, the interphase resistance difference becomes relativelysmall compared to a resistance value, and as a result, the interphasecurrent difference also becomes small. For this reason, since theamplitude of the secondary harmonic component (regarding the electricangle θ) included in the current gain value i_(q)/v_(q) or i_(q)/i_(q)*also becomes small, the detection precision of the peak electric angleθp obtained from the above angle-dependent data is reduced. Accordingly,it is preferable to determine a threshold value as an upper limit inadvance from the viewpoint of generation of heat as to the motor current(for example, the q-axis current detection value i_(q)), and tocalculate the current gain value i_(q)/v_(q) or i_(q)/i_(q)* to acquirethe angle-dependent data, so long as the detection value or instructionvalue of the motor current is smaller than the threshold value.

Additionally, in the above embodiment or the modification thereof, inorder to determine the correction coefficients g_(u), g_(v), and g_(w),the angle-dependent data regarding either the q-axis current gain valueor the d-axis current gain value is used. However, the angle-dependentdata regarding both of the q-axis current gain value and the d-axiscurrent gain value may be acquired so as to determine the correctioncoefficients g_(u), g_(v), and g_(w) based on the angle-dependent data.

In addition, in the above embodiment or the modification thereof, R, Φ,or the like which are used to calculate the d-axis voltage instructionvalue v_(d) and the q-axis voltage instruction value v_(q) in theopen-loop control unit 22 are treated as known parameters. However, thevalue calculated by the Φ calculating unit 26 is used as Φ. That is, Φis appropriately corrected by the Φ calculating unit 26 although beingtreated as a known parameter. However, the invention is not limited tothis. An R calculating unit may be provided instead of the Φ calculatingunit 26 or along with the Φ calculating unit 26, and when the d-axisvoltage instruction value v_(d) and the q-axis voltage instruction valuev_(q) are obtained, R calculated by the R calculating unit may be used(this point is also the same in the embodiments which will be describedlater). In addition, in a case where the R calculating unit is provided,the R calculating unit obtains the armature winding resistance Rincluded in the above Equations (1) and (2), using the followingequation based on the q-axis voltage instruction value v_(q), the d-axiscurrent detection value i_(d), the q-axis current detection value i_(q),and the angular velocity ω_(e) when i_(q)≠0.

R=(v _(q) −PL _(q) i _(q)−ω_(e) L _(d) i _(d)−ω_(e)Φ)/i _(q)

4. Second Embodiment

FIG. 8 is a block diagram showing the configuration of a motor controldevice related to a second embodiment of the invention. The motorcontrol device related to this embodiment is obtained by replacing themicrocomputer 20 and the current sensor 14 in the motor control devicerelated to the first embodiment with a microcomputer 30 and a currentsensor 15. This motor control device performs a feedback control whenthe current sensor 15 is normally operating, and performs an open loopcontrol when the current sensor 15 has failed.

The current sensors 15 are respectively provided on paths along which3-phase driving currents supplied to the brushless motor 1 flow, anddetects the 3-phase driving currents individually. 3-phase currentvalues (hereinafter referred to as a u-phase current detection valuei_(u), a v-phase current detection value i_(v), and a w-phase currentdetection value i_(w)) detected by the current sensors 15 are input tothe microcomputer 30.

The microcomputer 30 is obtained by adding a 3-phase/dq-axis converter31, a subtraction unit 32, a feedback control unit 33, a failuremonitoring unit 34, and an instruction voltage selecting unit 35 to themicrocomputer 20. Additionally, even in the microcomputer 30, similarlyto the above first embodiment, a correction unit 50 including the dataacquisition unit 41, the correction coefficient determining unit 42, anda correction executing unit 53 is realized. However, the functions ofthe correction executing unit 53 are slightly different from those ofthe above first embodiment (the details thereof will be describedbelow).

The 3-phase/dq-axis converter 31 calculates the d-axis current detectionvalue i_(d) and the q-axis current detection value i_(q), using thefollowing Equations (16) and (17), based on the u-phase currentdetection value i_(u) and the v-phase current detection value i_(v)which have been detected by the current sensors 15.

i _(q)=√2×{i _(v)×sin θ−i _(u)×sin(θ−2π/3)}  (16)

i _(q)=2×{i _(v)×cos θ−i _(u)×cos(θ−2π/3)}  (17)

The subtraction unit 32 obtains a deviation E_(d) between the d-axiscurrent instruction value i_(d)* and the d-axis current detection valuei_(d), and a deviation E_(q) between the q-axis current instructionvalue i_(q)* and the q-axis current detection value i_(q). The feedbackcontrol unit 33 performs the proportional integral operation shown inthe following Equations (18) to (19) on the deviations E_(d) and E_(q),and obtains a d-axis voltage instruction value v_(d) ^(#) and a q-axisvoltage instruction value v_(q) ^(#).

v _(d) ^(#) =K×{E _(d)+(1/T)∫E _(d) ·dt}  (18)

v _(q) ^(#) =K×{E _(q)+(1/T)∫E _(q) ·dt}  (19)

Here, K is a proportional gain constant, and T is integral time inEquations (18) and (19).

The failure monitoring unit 34 examines whether or not the 3-phasecurrent values detected by the current sensors 15 are within a normalrange, and determines whether the current sensors 15 are normallyoperating or fail. The failure monitoring unit 34 determines the currentsensors to be “Normal”, when all the 3-phase current values are within anormal range, and determines a current sensor to be “Failure” whencurrent values of one or more phases are out of a normal range. Thefailure monitoring unit 34 outputs a control signal showingdetermination result.

When the current sensors are determined to be normal in the failuremonitoring unit 34, the instruction voltage selecting unit 35 outputsthe d-axis voltage instruction value v_(d) ^(#) and q-axis voltageinstruction value v_(q) ^(#) which have been obtained in the feedbackcontrol unit 33, and when a current sensor is determined to fail in thefailure monitoring unit 34, the instruction voltage selecting unitoutputs the d-axis voltage instruction value v_(d) and q-axis voltageinstruction value v_(q) which have been calculated by the open-loopcontrol unit 22.

When the current sensors 15 are normally operating, the failuremonitoring unit 34 determines that the current sensors are normal, andthe instruction voltage selecting unit 35 selects the output of thefeedback control unit 33. At this time, the instruction currentcalculating unit 21, the dq-axis/3-phase conversion unit 23, the anglecalculating unit 24, the 3-phase/dq-axis converter 31, the subtractionunit 32, and the feedback control unit 33 operate, and the feedbackcontrol is performed. In addition to this, while the current sensors 15are normally operating, the angular velocity calculating unit 25 and theΦ calculating unit 26 also operate. The Φ calculating unit 26 obtainsthe armature winding interlinking magnetic flux number Φ included inEquation (2), using Equation (15), while the current sensors 15 arenormally operating.

The data acquisition unit 41 and the correction coefficient determiningunit 42 also operate while the current sensors 15 are normallyoperating, similarly to the above first embodiment. That is, the dataacquisition unit 41 acquires the angle-dependent data showing the q-axiscurrent gain value i_(q)/v_(q) ^(#) to various electric angles θ, usingthe q-axis current detection value i_(q) calculated based on the u-phasecurrent detection value i_(u) and the v-phase current detection valuei_(v) from the current sensors 15, the q-axis voltage instruction valuev_(q) ^(#) from the feedback control unit 33, and the electric angle θfrom the angle calculating unit 24. Additionally, the correctioncoefficient determining unit 42 determines the correction coefficientsg_(u), g_(v), and g_(w) based on the angle-dependent data. Thecorrection coefficients g_(u), g_(v), and g_(w) are given to thecorrection executing unit 53. Similarly to the above first embodiment,along with the correction coefficients g_(u), g_(v), and g_(w), thearmature winding interlinking magnetic flux number Φ is given to thecorrection executing unit 53 from the Φ calculating unit 26, and theangular velocity ω_(e) is given to the correction executing unit fromthe angular velocity calculating unit 25. Moreover, a control signalshowing a determination result in the failure monitoring unit 34 is alsogiven to the correction executing unit 53.

Meanwhile, while the current sensors 15 are normally operating, thefeedback control is performed so that the deviation E_(d) between thed-axis current instruction value i_(d)* and the d-axis current detectionvalue i_(d) and the deviation E_(q) between the q-axis currentinstruction value i_(q)* and the q-axis current detection value i_(q)are cancelled. Therefore, generally, the generation of the torque rippleresulting from the interphase resistance difference does not become aproblem. Thus, in this embodiment, the correction executing unit 53gives the phase voltage instruction values V_(u), V_(v), and V_(w),which are output from the dq-axis/3-phase conversion unit 23, to the3-phase/PWM modulator 12 as they are, without correcting the phasevoltage instruction values while the current sensors 15 are normallyoperating, i.e., while the feedback control is performed, based on theabove control signal from the failure monitoring unit 34. That is,V_(u)=V_(uc), V_(v)=V_(vc), and V_(w)=V_(wc) are established. However,even while the feedback control is performed, the phase voltageinstruction values V_(u), V_(v), and V_(w) may be corrected using theabove correction coefficients g_(u), g_(v), and g_(w).

Thereafter, when the current sensors 15 fail, the failure monitoringunit 34 determines that a current sensor have failed, and theinstruction voltage selecting unit 35 selects the output of theopen-loop control unit 22. At this time, the instruction currentcalculating unit 21, the open-loop control unit 22, the dq-axis/3-phaseconversion unit 23, and the angle calculating unit 24 operate, and theopen loop control is performed. The open-loop control unit 22 obtainsthe d-axis voltage instruction value v_(d) and the q-axis voltageinstruction value v_(q), using the Φ value obtained while the currentsensors 15 are normally operating. The d-axis voltage instruction valuev_(d) and the q-axis voltage instruction value v_(q) are given to thedq-axis/3-phase conversion unit 23 via the instruction voltage selectingunit 35, and are converted into the phase voltage instruction valuesV_(u), V_(v), and V_(w) in the instruction voltage selecting unit. Thephase voltage instruction values V_(u), V_(v), and V_(w) are given tothe correction executing unit 53.

The correction executing unit 53 corrects the phase voltage instructionvalues V_(u), V_(v), and V_(w) according to Equations (7) to (12) asmentioned earlier, using the correction coefficients g_(u), g_(v), andg_(w) from the correction coefficient determining unit 42, the armaturewinding interlinking magnetic flux number Φ from the Φ calculating unit26, and the angular velocity ω_(e) from the angular velocity calculatingunit 25, similarly to the above first embodiment, when a current sensor15 fails, based on the control signal from the failure monitoring unit34. The phase voltage instruction values V_(uc), V_(vc), and V_(wc)after this correction are given to the 3-phase/PWM modulator 12. A motordriving means including the 3-phase/PWM modulator 12 and the motor drivecircuit 13 drives the brushless motor 1 by the voltages of the phasevoltage instruction values V_(uc), V_(vc), and V_(wc).

As shown above, the motor control device related to this embodimentobtains the voltage instruction values by performing proportionalintegral operation on the differences between the current instructionvalues and the current values detected by the current sensors when thecurrent sensors are normally operating, and obtains the voltageinstruction values by performing the open loop control according to thecircuit equations of the motor, based on the current instruction valuesand the angular velocity of the rotor, when a current sensor has failed.Additionally, when the open loop control is performed, the Φ value (thearmature winding interlinking magnetic flux number Φ) obtained while thecurrent sensors are normally operating is used. Accordingly, accordingto the motor control device related to this embodiment, while thecurrent sensors are normally operating, the feedback control can beperformed to drive the brushless motor with high precision.Additionally, when a current sensor fails, and the feedback controlcannot be performed, the brushless motor can be driven with highprecision to obtain a desired motor output, by performing the open loopcontrol, using the armature winding interlinking magnetic flux number Φobtained while the feedback control is performed.

Additionally, according to this embodiment, in a case where the openloop control is performed, the phase voltage instruction values arecorrected by the correction executing unit 53 so that the dependency ofthe q-axis current i_(q) or d-axis current i_(d) on the electric angle θis reduced or eliminated using the correction coefficients obtained bythe data acquisition unit 41 and the correction coefficient determiningunit 42. This suppresses generation of the torque ripple resulting fromthe interphase resistance difference. Accordingly, even in a case wherea current sensor fails, and the feedback control cannot be performed, afavorable steering feel can be obtained.

In addition, even in this embodiment, the same modifications as themodification of the above first embodiment can be made to the dataacquisition unit 41 and the correction coefficient determining unit 42.

5. Other Embodiments

Although only one current sensor 14 is provided in the above firstembodiment or modification, a plurality of (two or three) may beprovided. For example, in a case where current sensors for u-phase andv-phase are provided, the d-axis current detection value i_(d) andq-axis current detection value i_(q) which are used in the dataacquisition unit 41 and the Φ calculating unit 26 are obtained byconverting the u-phase current detection value i_(u) and v-phase currentdetection value i_(v) which are output from the current sensors foru-phase and v-phase into the current values on the dq coordinate axes.

Additionally, in the motor control device related to the secondembodiment, the feedback control and the open loop control are switchedto each other by the determination result in the failure monitoring unit34. However, the feedback control and the open loop control may beswitched to each other by determination (for example, by driver'sselection) other than determination in the failure monitoring unit 34.

In addition, the invention can be applied not only to the above-descriedcolumn assist type electric power steering device but also a pinionassist type or rack assist type electric power steering device.Additionally, the invention can also be applied to motor control devicesother than the electric power steering device.

6. Third Embodiment

Next, a motor control device related to a third embodiment of theinvention will be described referring to FIGS. 9 to 11.

In addition, the third embodiment is mainly different from the firstembodiment in that the microcomputer functions as a phase currentcalculating unit 141, a storage unit 142, a phase resistance calculatingunit 143, and a correction unit 144, instead of the data acquisitionunit 41, the correction coefficient determining unit 42, and thecorrection executing unit 43 in the first embodiment. In the followingdescription, the same reference numerals will be given to the samecomponents as the first embodiment, and the descriptions thereof areomitted.

In this embodiment a current detecting means which detects the u-phase,v-phase, and w-phase currents I_(u), I_(v), and I_(w) of the brushlessmotor 1 is constituted by the current sensor 14, and the phase currentcalculating unit 41 which will be described later.

According to the third embodiment, while the brushless motor 1 isrotating, 3-phase driving currents can be detected using one currentsensor 14. Thus, in this embodiment, the phase current calculating unit141 calculates the values (hereinafter, referred to as a “u-phasecurrent detection value I_(u),” a “v-phase current detection valueI_(v),” and a w-phase current detection value I_(w), and genericallyreferred to respective current detection values I_(u), I_(v), and I_(w))of the u-phase, v-phase, and w-phase currents which flow into thebrushless motor 1 from the current value I_(a) detected by the currentsensor 14. Additionally, the storage unit 142 stores the phase voltageinstruction value V_(uc), V_(vc), and V_(wc) after correction at thetime of the detection of respective phase current detection value I_(x)(x=u, v, and w), i.e., at the time of the detection of the current valueI_(a) used for the calculation of the respective phase current detectionvalue I_(x). In the following, the phase voltage instruction valuesV_(uc), V_(vc), and V_(wc) after correction at the time of the detectionof the x-phase current detection value I_(x) are shown by symbols“V_(ux)”, “V_(vx)”, and “V_(wx)”, respectively (x=u, v, and w).

The phase resistance calculating unit 143 obtains the values of theu-phase resistance R_(u), the v-phase resistance R_(v), and the w-phaseresistance R_(w) (refer to FIG. 10), based on the respective phasecurrent detection value I_(x) detected by a current detecting meansincluding the above phase current calculating unit 141 and currentsensor 14, and the phase voltage instruction value V_(ux), V_(vx), andV_(wx) (x=u, v, and w) after correction at the time of the detection ofthe respective phase current detection values. Here, the u-phaseresistance, the v-phase resistance, and the w-phase resistance meancircuit resistances including armature winding resistances regardingu-phase, v-phase, and w-phase, respectively, and are shown by symbols“R_(u)”, “R_(v)”, and “R_(w)”, respectively. Additionally, the symbols“R_(u)”, “R_(v)”, and “R_(w)” shall also show the values of the u-phaseresistance, the v-phase resistance, and the w-phase resistance,respectively. In addition, in the following, the u-phase resistance, thev-phase resistance, and the w-phase resistance are also collectivelyreferred to as a “phase resistances”. The wiring resistance between thebrushless motor 1 and the ECU 10, the resistances and wiring resistanceswithin of the motor drive circuit 13 within the ECU 10, or the like areincluded in circuit resistances equivalent to these phase resistances.This point is also the same in the other embodiments. The details of acalculation method of the phase resistances R_(u), R_(v), and R_(w) inthe phase resistance calculating unit 143 will be described later.

The values of the phase resistances R_(u), R_(v), and R_(w) calculatedby the phase resistance calculating unit 143, the armature windinginterlinking magnetic flux number Φ calculated by the Φ calculating unit26, and the angular velocity ω_(e) calculated by the angular velocitycalculating unit 25 are input to the correction unit 144, and thecorrection unit 144 corrects the phase voltage instruction values V_(u),V_(v), and V_(w) according to the following Equations (20) to (22).

V _(uc)=(V _(u) −e _(u))·R _(u) /R _(r) +e _(u)  (20)

V _(vc)=(V _(v) −e _(v))·R _(v) /R _(r) +e _(v)  (21)

V _(wc)=(V _(w) −e _(w))·R _(w) /R _(r) +e _(w)  (22)

In the above Equations (20) to (22), R_(r) is a resistance value(hereinafter referred to as a “reference resistance value”) to be areference set common to the respective phases. As this referenceresistance value R_(r), for example, an average value of the respectivephase resistances can be used, and the resistance value of a specificphase at a predetermined point of time may be used. Moreover, thereference resistance value R_(r) may not necessarily be a fixed value.In addition, when the values of the phase resistances R_(u), R_(v), andR_(w) are not yet calculated, the value of the reference resistancevalue R_(r) may be determined in advance, and the phase voltageinstruction values V_(uc), V_(vc), and V_(wc) after correction may becalculated as R_(u)=R_(v)=R_(w)=R_(r).

In the above Equations (20) to (22), e_(u), e_(v), and e_(w) arecalculated from Equations (11) to (13) similarly to the firstembodiment. Additionally, since the armature winding interlinkingmagnetic flux number Φ by the Φ calculating unit 26 can be calculatedsimilarly to the first embodiment, the voltage instruction values can beobtained using the Φ value.

Through the above configuration, according to the second embodiment, thesame effects as the first embodiment can be obtained.

In addition, in the second embodiment, R, Φ, or the like which are usedto calculate the d-axis voltage instruction value v_(d) and the q-axisvoltage instruction value v_(q) in the open-loop control unit 22 aretreated as known parameters. However, the value calculated by the Φcalculating unit 26 is used as Φ. That is, Φ is appropriately correctedby the Φ calculating unit 26 serving as a parameter calculation meansalthough being treated as a known parameter. However, the invention isnot limited to this configuration. An R calculating unit serving as aparameter calculation means may be provided instead of the Φ calculatingunit 26 or along with the Φ calculating unit 26, and when the d-axisvoltage instruction value v_(d) and the q-axis voltage instruction valuev_(q) are obtained, R calculated by the R calculating unit may be used(this point is also the same in other embodiments which will bedescribed later). In addition, in a case where the R calculating unit isprovided, the R calculating unit obtains the armature winding resistanceR included in the above Equations (1) and (2), using the followingequation based on the q-axis voltage instruction value v_(q), the d-axiscurrent detection value i_(d), the q-axis current detection value i_(q),and the angular velocity ω_(e) when i_(q)≠0.

R=(v _(q) −PL _(q) i _(q)−ω_(e) L _(d) i _(d)−ω_(e)Φ)/i _(q)

Next, a calculation method of the phase resistances R_(u), R_(v), andR_(w) in the phase resistance calculating unit 143 will be described. Inthis embodiment, when the temporal change of an x-phase current isloose, the x-phase current is detected, and a voltage drop caused by thex-phase inductance is negligible (x=u, v, and w). In this case, when theu-phase, v-phase, and w-phase counter-electromotive forces (inducedvoltages) in the brushless motor 1 at the time of the detection of thex-phase current detection value I_(x) are shown by “E_(ux)”, “E_(vx)”,and “E_(wx)”, respectively, and the u-phase, v-phase, and w-phasecurrent values at the time of the detection of the x-phase currentdetection value I_(x) are shown by “I_(ux)”, “I_(vx)”, and “I_(wx)”,respectively (x=u, v, and w), the following equations are established.

V _(uu) =I _(uu) ·R _(u) +E _(uu)  (23a)

V _(vu) =I _(vu) ·R _(v) +E _(vu)  (23b)

V _(wu) =I _(wu) ·R _(w) +E _(wu)  (23c)

V _(uv) =I _(uv) ·R _(u) +E _(uv)  (24a)

V _(vv) =I _(vv) ·R _(v) +E _(vv)  (24b)

V _(wv) =I _(wv) ·R _(w) +E _(wv)  (24c)

V _(uw) =I _(uw) ·R _(u) +E _(uw)  (25a)

V _(vw) =I _(vw) ·R _(v) +E _(vw)  (25b)

V _(ww) =I _(ww) ·R _(w) +E _(ww)  (25c)

I _(uu) +I _(vu)+_(wu)=0  (26a)

I _(uv) +I _(vv) +I _(wv)=0  (26b)

I _(uw) +I _(vw) +I _(ww)=0  (26c)

E _(uu) +E _(vu) +E _(wu)=0  (27a)

E _(uv) +E _(vv) +E _(wv)=0  (27b)

E _(uw) +E _(vw) +E _(ww)=0  (27c)

V _(uu) +V _(vu) +V _(wu)=0  (28a)

V _(uv) +V _(vv) +V _(wv)=0  (28b)

V _(uw) +V _(vw) +V _(ww)=0  (28c)

In the above eighteen Equations (23a) to (28c), the phase voltageinstruction values V_(ux), V_(vx), and V_(wx) (x=u, v, and w) and thephase current detection values I_(uu), I_(vv), and I_(ww) are known, andthe phase resistances R_(u), R_(v), and R_(w), the phase current valuesI_(vu), I_(wu), I_(uv), l_(wv), I_(uw), and I_(vw) and the inducedvoltages E_(ux), E_(vx), and E_(wx) (x=u, v, and w) are eighteenunknowns. Thus, the phase resistances R_(u), R_(v), and R_(w) can beobtained from the above Equations (23a) to (28c). Specifically, thephase resistances R_(u), R_(v), and R_(w) are obtained as follows.

When the u-phase current is detected, the phase current calculating unit141 outputs the u-phase current detection value I_(u), the storage unit142 stores the u-phase, v-phase, and w-phase voltage instruction valuesV_(uc), V_(vc), and V_(wc) after correction at the time of the detectionas V_(uu), V_(vu), and V_(wu), respectively. The phase resistancecalculating unit 143 obtains U_(a) and U_(b) given by the followingequations, using the u-phase current detection value I_(u), and thephase voltage instruction values V_(uu), V_(vu), and V_(wu) at the timeof the detection when I_(u)≠0.

U _(a)=(V _(uu) −V _(vu))/I _(u)  (29a)

U _(b)=(V _(uu) −V _(wu))/I _(u)  (29b)

When the v-phase current is detected, the phase current calculating unit141 outputs the v-phase current detection value I_(v), the storage unit142 stores the u-phase, v-phase, and w-phase voltage instruction valuesV_(uc), V_(vc), and V_(wc) after correction at the time of the detectionas V_(uv), V_(vv), and V_(wv), respectively. The phase resistancecalculating unit 143 obtains V_(a) and V_(b) given by the followingequations, using the v-phase current detection value I_(v), and thephase voltage instruction values V_(uv), V_(vv), and V_(wv) at the timeof the detection when I_(v)≠0.

V _(a)=(V _(vv) −V _(wv))/I _(v)  (30a)

V _(b)=(V _(vv) −V _(uv))/I _(v)  (30b)

When the w-phase current is detected, the phase current calculating unit141 outputs the w-phase current detection value I_(w), the storage unit142 stores the u-phase, v-phase, and w-phase voltage instruction valuesV_(uc), V_(vc), and V_(wc) after correction at the time of the detectionas V_(uw), V_(vw), and V_(ww), respectively. The phase resistancecalculating unit 143 obtains W_(a) and W_(b) given by the followingequations, using the w-phase current detection value I_(w), and thephase voltage instruction values V_(uw), V_(vw), and V_(ww) at the timeof the detection when I_(w)≠0.

W _(a)=(V _(ww) −V _(uw))/I _(w)  (31a)

W _(b)=(V _(ww) −V _(vw))/I _(w)  (31b)

Next, r_(a), r_(b), r_(c), and r_(d) given by the following equationsare calculated using the calculated U_(a), U_(b), V_(a), V_(b), W_(a),and W_(b).

r _(a) =U _(a) ·V _(a) ·W _(a) −U _(b) ·V _(b) ·W _(b)  (32a)

r _(b) =W _(a) ·U _(a) −W _(a) ·V _(b) +U _(b) ·V _(b)  (32b)

r _(c) =U _(a) ·V _(a) −U _(a) ·W _(b) +V _(b) ·W _(b)  (32c)

r _(d) =V _(a) ·W _(a) −V _(a) ·U _(b) +W _(b) ·U _(b)  (32d)

Next, the phase resistances R_(u), R_(v), and R_(w) are calculated bythe following equations, using the calculated r_(a), r_(b), r_(c), andr_(d).

R _(u) =r _(a) ·r _(b)/(r _(b) ·r _(c) +r _(c) ·r _(d) +r _(d) ·r_(b))  (33a)

R _(v) =r _(a) ·r _(c)/(r _(b) ·r _(c) +r _(c) ·r _(d) +r _(d) ·r_(b))  (33b)

R _(w) =r _(a) ·r _(d)/(r _(b) ·r _(c) +r _(c) ·r _(d) +r _(d) ·r_(b))  (33c)

The values of the phase resistance R_(u), R_(v), and R_(w) required forcorrection of the phase voltage instruction values V_(u), V_(v), andV_(w) according to Equations (20) to (22) as mentioned earlier can becalculated described above when the u-phase, v-phase, and w-phasecurrent detection values I_(u), I_(v), and I_(w) are detected. Howeverwhen an electric current which flows into the brushless motor 1, thecalculation accuracy of the phase resistances R_(u), R_(v), and R_(w) isdegraded due to generation of heat. Hereinafter, this point will bedescribed.

Now, the difference of the v-phase resistance R_(v) from the u-phaseresistance R_(u) is set to 1 mΩ, and the difference of the w-phaseresistance R_(w) from the u-phase resistance R_(u) is set to 2 mΩ. Inthis case, if R_(u)=10 mΩ, R_(v)=11 mΩ and R_(w)=12 mΩ are obtained.Accordingly, resistance ratios R_(v)/R_(u) and R_(w)/R_(u) are obtainedas follows:

R _(v) /R _(u)=11/10=1.1, and

R _(w) /R _(u)=12/10=1.2.

Thus, when the resistance differences are shown by relative values, thedifference of the v-phase resistance R, from the u-phase resistanceR_(u) is 10%, and the difference of the w-phase resistance R_(w) fromthe u-phase resistance R_(u) is 20%.

Generally, the interphase resistance differences are not influenced bygeneration of heat caused by an electric current which flows into themotor. For this reason, supposing that the u-phase resistance Rubecomes, for example, R_(u)=20 mΩ by generation of heat caused by anelectric current, R_(v)=21 mΩ and R_(w)=22 mΩ are obtained. Sinceresistance ratios R_(v)/R_(u) and R_(w)/R_(u) at this time are

R _(v) /R _(u)=21/20=1.05, and

R _(w) /R _(u)=22/20=1.1,

when the resistance differences are shown by relative values, thedifference of the v-phase resistance R_(v) from the u-phase resistanceR_(u) becomes 5%, and the difference of the w-phase resistance R_(w)from the u-phase resistance R_(u) becomes 10%.

In this way, when the resistance values become large due to generationof heat caused by an electric current, the interphase resistancedifferences become relatively small. Accordingly, as seen from theviewpoint of the interphase resistance differences, generation of heatcaused by an electric current degrades the calculation accuracy of thephase resistances. Hence, it is preferable to calculate the phaseresistances when generation of heat caused by an electric current issmall. Thus, in this embodiment, when the instruction value or detectionvalues of the u-phase, v-phase, and w-phase currents are smaller thanpredetermined threshold values, the phase resistances R_(u), R_(v), andR_(w) are calculated as described above. Hereinafter, the operation ofthe phase resistance calculating unit 143 in this embodiment will bedescribed.

FIG. 11 is a flow chart for explaining an example of the operation ofthe phase resistance calculating unit in the third embodiment. In thisexample of operation, the phase resistance calculating unit 143calculates the phase resistances R_(u), R_(v), and R_(w) according tothe following procedure. As earlier mentioned, whenever any one of theu-phase, v-phase, and w-phase current detection values is calculatedfrom the current detection value I_(a) from obtained by the currentsensor 14, the phase current calculating unit 141 gives the phasecurrent detection value I_(x) to the phase resistance calculating unit143 (x is any one of u, v, and w), and the phase resistance calculatingunit 143 receives the phase current detection value I_(x) sequentially(Step S10). The phase resistance calculating unit 143 returns to StepS10 if the received phase current detection value I_(x) are zero, andreceives the phase current detection values I_(y) to be calculated next(y is any one of u, v, and w). By repeating Steps S10 and S12 in thisway, when the u-phase, v-phase and w-phase current detection valuesI_(u), I_(v), and I_(w) which are not zero are received, the phaseresistance calculating unit 143 determines whether or not all absolutevalues |I_(u)|, |I_(v)|, and |I_(w)| of the phase current detectionvalues are smaller than a predetermined threshold I_(th), and as aresult, returns to Step S10 if any one of |I_(u)|, |I_(v)|, and |I_(w)|is equal to or more than the threshold value I_(th), or proceeds to StepS16 if all of |I_(u)|, |I_(v)|, and |I_(w)| are smaller than thethreshold value I_(th). Here, the threshold value I_(th) is introducedin order to prevent degradation of the calculation accuracy of the phaseresistances due to generation of heat caused by an electric current asmentioned earlier, and is set so that the phase resistances arecalculated within a range where an increase in phase resistance causedby generation of heat is comparatively small. The concrete value of thethreshold value changes depending on brushless motors, and motor controldevices which drive the motors, and are practically determined usingexperiments regarding individual brushless motors and motor controldevices, computer simulation, or the like.

When the processing has proceeded to Step S16, the phase currentdetection value I_(x) (x=u, v, and w) all of which are not zero, and theabsolute values of which are smaller than the threshold value I_(th) areobtained. The phase resistance calculating unit 143 takes out therespective phase voltage instruction values V_(ux), V_(vx), and V_(wx)(after correction) at the time of the detection of the respective phasecurrent detection value I_(x) from the storage unit 142, and calculatesthe phase resistances R_(u), R_(v), and R_(w) based on Equations (29a)to (33c) as earlier mentioned, using the respective phase voltageinstruction values V_(ux), V_(vx), and V_(wx) (x=u, v, and w), and theabove respective phase current detection value I_(x).

The calculation values of the phase resistances R_(u), R_(v), and R_(w)obtained as described above are given to the correction unit 144 fromthe phase resistance calculating unit 143 (Step S20). The correctionunit 144 corrects the phase voltage instruction values V_(u), V_(v), andV_(w) based on Equations (20) to (22) as earlier mentioned, using thecalculation values of the phase resistances R_(u), R_(v), and R_(w).

After the phase resistances R_(u), R_(v), and R_(w) are calculated inthis way, the processing returns to Step S10 in order to calculate thephase resistances R_(u), R_(v), and R_(w) based on the respective newphase current detection value I_(x).

In addition, the operation of the phase resistance calculating unit 143according to the procedure shown in FIG. 11 is an example, and theoperation of the phase resistance calculating unit 143 is not limited tosuch a procedure. For example, the processing of Steps S10 to S20 shownin FIG. 11 may be executed at predetermined time intervals.Additionally, the processing of Steps S10 to S20 shown in FIG. 11 may beexecuted only once after the start of driving of the brushless motor 1,and may be executed when the state of temperature or the like haschanged.

In the example of operation shown in FIG. 11, if the determinationresult of Step S12 is “No”, and the determination result of Step S14 is“Yes”, the instruction values V_(ux), V_(vx), and V_(wx) of therespective phase voltages at the time of the detection of the respectivephase currents are taken out from the storage unit 142. Instead of this,however, whenever any one phase current detection value I_(x) isobtained, it may be determined whether or not the phase currentdetection value I_(x) is not zero and the absolute value thereof issmaller than the threshold value I_(th). Then, if the phase currentdetection value I_(x) is not zero, and the absolute value thereof issmaller than the threshold value I_(th), in-between parameter valuesX_(a) and X_(b) corresponding to the current detection values I_(x),(x=u, v, and w; X=U, V, and W) may be calculated based on Equations(29a) and (29b); (30a) and (30b); or (31a) and (31b).

Additionally, in the example of operation shown in FIG. 11, it isdetermined in Step S14 whether or not the absolute values of thedetection values of the respective phase currents are smaller than thethreshold value I_(th). Instead of this, however, it may be determinedwhether or not the absolute values of the instruction values of therespective phase currents are smaller than the threshold value I_(th).In this case, the instruction values of the respective phase currentscan be obtained by converting the d-axis and q-axis current instructionvalues i_(d)*, and i_(q)* acquired by the instruction currentcalculating unit 21 into values on the 3-phase alternating-currentcoordinate axes. Additionally, instead of these, it may be determinedwhether or not the absolute values or square sum of the d-axis andq-axis current instruction values i_(d)*, and i_(q)* are smaller than apredetermined threshold value. More generally, when the magnitude of anelectric current which flows into the brushless motor 1 is smaller thana predetermined value, the phase resistances R_(u), R_(v), and R_(w) maybe calculated, so that degradation in the phase resistance calculationaccuracy resulting from generation of heat caused by an electric currentcan be prevented.

Additionally, even if the absolute values of the respective phasecurrent values are smaller than a threshold value predetermined, andgeneration of heat is small, if the respective phase current valuesI_(u), I_(v), and I_(w) in Equations (29a) to (31b) are close to zero,an error is apt to occur. Thus, in addition to the determination of StepS14, it may be determined whether or the not absolute values |I_(u)|,|I_(v)|, and |I_(w)| of the respective phase current detection valuesare greater than another threshold value I_(th2) (here, I_(th)>I_(th2)),and only if the absolute values are greater than the threshold valueI_(th2), the phase resistances may be calculated.

As described above, according to this embodiment, the phase resistancesR_(u), R_(v), and R_(w) are calculated using the detection values I_(x)of the respective phase currents, and the instruction values V_(ux),V_(vx), and V_(wx) (x=u, v, and w) of the respective phase voltages atthe time of the detection, and the instruction values V_(y) of therespective phase voltages at this time are corrected according to thevalues of the phase resistances R_(y) (y=u, v, and w). That is, therespective phase voltage instruction values V_(u), V_(v), and V_(w) arecorrected according to Equations (20) to (22), using the calculationvalues of the phase resistances R_(u), R_(v), and R_(w). Here, Equations(20) to (22) show that the respective phase voltage instruction valuesV_(y) are corrected so that portions equivalent to applied voltages tothe phase resistances R_(y) among the respective phase voltageinstruction values V_(y) are proportional to the values of theresistances R_(y) (y=u, v, and w). An interphase resistance differenceis compensated by such correction, and the torque ripple resulting fromthe interphase resistance difference is reduced. Accordingly, accordingto the electric power steering device using the motor control devicerelated to this embodiment, the output torque of the motor becomessmooth, and the steering feel is improved.

Moreover, according to this embodiment, the values of the phaseresistances R_(u), R_(v), and R_(w) used for correction of the phasevoltage instruction values are calculated when the respective phasecurrents are small and an increase in resistance value caused bygeneration of heat is small. Thus, the phase resistances R_(u), R_(v),and R_(w) are calculated with high precision. Thereby, compensation ofthe interphase resistance differences by correction of the phase voltageinstruction values is more accurately performed, and as a result, thetorque ripple can be sufficiently reduced.

7. Fourth Embodiment

FIG. 12 is a block diagram showing the configuration of a motor controldevice related to a fourth embodiment of the invention. The motorcontrol device related to this embodiment is obtained by replacing themicrocomputer 20 and the current sensor 14 in the motor control devicerelated to the third embodiment with a microcomputer 30 and a currentsensor 15. This motor control device performs a feedback control whenthe current sensor 15 is normally operating, and performs an open loopcontrol when the current sensor 15 has failed. That is, the fourthembodiment is the same as the second embodiment to the first embodiment.In the following description, the same reference numerals will be givento the same components as the second embodiment, and the descriptionsthereof are omitted.

Even in the microcomputer 30, the phase resistance calculating unit 153and the correction unit 154 are included similarly to the above thirdembodiment. In this embodiment, however, the 3-phase driving currentssupplied to the brushless motor 1 are individually detected. Therefore,the phase current calculating unit 141 and the storage unit 142 are notincluded.

While the current sensors 15 are normally operating, the phaseresistance calculating unit 53 calculates the phase resistances R_(u),R_(v), and R_(w) similarly to the above third embodiment. That is, thephase resistance calculating unit 143 obtains the values of the u-phaseresistance R_(u), the v-phase resistance R_(v), and the w-phaseresistance R_(w) in the brushless motor 1, based on the respective phasecurrent detection values I_(u), I_(v), and I_(w) detected by the currentsensors 15, and the phase voltage instruction values V_(uc), V_(vc), andV_(wc) after correction at the time of the detection. Here, the u-phase,v-phase, and w-phase current detection values I_(u), I_(v), and I_(w)are simultaneously detected. For this reason, the phase voltageinstruction values V_(uc), V_(vc), and V_(wc) at the time of the abovedetection correspond to the respective phase voltage instruction valuesV_(ux), V_(vx), and V_(wx) (x=u, v, and w) at the time of the detectionof the respective phase currents in the first embodiment. Accordingly,if “V_(ux), V_(vx), and V_(wx) (x=u, v, and w)” in the flow chart shownin FIG. 11 are replaced with “V_(uc), V_(vc), and V_(wc)”, this flowchart shows the example of operation in this embodiment. Thus, thedetailed description regarding the phase resistance calculating unit 53is omitted.

The calculation values of the phase resistance R_(u), R_(v), and R_(w)obtained by the phase resistance calculating unit 53 are given to thecorrection unit 54. Similarly to the above first embodiment, along withthe calculation values of the phase resistances R_(u), R_(v), and R_(w),the armature winding interlinking magnetic flux number Φ is given to thecorrection unit 54 from the Φ calculating unit 26, and the angularvelocity ω_(e) is given to the correction unit from the angular velocitycalculating unit 25. Moreover, a control signal showing a determinationresult in the failure monitoring unit 34 is also given to the correctionunit 54.

Meanwhile, while the current sensors 15 are normally operating, thefeedback control is performed so that the deviation E_(d) between thed-axis current instruction value i_(d)* and the d-axis current detectionvalue i_(d) and the deviation E_(q) between the q-axis currentinstruction value i_(d)* and the q-axis current detection value i_(q)are cancelled. Therefore, generally, the generation of the torque rippleresulting from the interphase resistance difference does not become aproblem. Thus, in this embodiment, the correction unit 54 gives thephase voltage instruction values V_(u), V_(v), and V_(w), which areoutput from the dq-axis/3-phase conversion unit 23, to the 3-phase/PWMmodulator 12 as they are, without correcting the phase voltageinstruction values while the current sensors 15 are normally operating,i.e., while the feedback control is performed, based on the abovecontrol signal from the failure monitoring unit 34. That is,V_(u)=V_(uc), V_(v)=V_(vc), and V_(w)=W_(wc) are established. However,even while the feedback control is performed, the phase voltageinstruction values V_(u), V_(v), and V_(w) may be corrected using thecalculation values of the above phase resistances R_(u), R_(v), andR_(w).

Thereafter, when the current sensors 15 fail, the failure monitoringunit 34 determines that a current sensor have failed, and theinstruction voltage selecting unit 35 selects the output of theopen-loop control unit 22. At this time, the instruction currentcalculating unit 21, the open-loop control unit 22, the dq-axis/3-phaseconversion unit 23, and the angle calculating unit 24 operate, and theopen loop control is performed. The open-loop control unit 22 obtainsthe d-axis voltage instruction value v_(d) and the q-axis voltageinstruction value v_(q), using the Φ value obtained while the currentsensors 15 are normally operating. The d-axis voltage instruction valuev_(d) and the q-axis voltage instruction value v_(q) are given to thedq-axis/3-phase conversion unit 23 via the instruction voltage selectingunit 35, and are converted into the phase voltage instruction valuesV_(u), V_(v), and V_(w) in the instruction voltage selecting unit. Thephase voltage instruction values V_(u), V_(v), and V_(w) are given tothe correction unit 54.

The correction unit 54 corrects the phase voltage instruction valuesV_(u), V_(v), and V_(w) according to Equations (20) to (22) as mentionedearlier, using the calculation values of the phase resistance R_(u),R_(v), and R_(w) from the phase resistance calculating unit 53, thearmature winding interlinking magnetic flux number Φ from the Φcalculating unit 26, and the angular velocity ω_(e) from the angularvelocity calculating unit 25, similarly to the above first embodiment,when a current sensor 15 fails, based on the control signal from thefailure monitoring unit 34. The phase voltage instruction values V_(uc),V_(vc), and V_(wc) after this correction are given to the 3-phase/PWMmodulator 12. A motor driving means including the 3-phase/PWM modulator12 and the motor drive circuit 13 drives the brushless motor 1 by thevoltages of the phase voltage instruction values V_(uc), V_(vc), andV_(wc).

As shown above, similarly to the second embodiment, when a currentsensor fails, and the feedback control cannot be performed, thebrushless motor can be driven with high precision to obtain a desiredmotor output, by performing the open loop control, using the armaturewinding interlinking magnetic flux number Φ obtained while the feedbackcontrol is performed.

Additionally, according to the fourth embodiment, in a case where theopen loop control is performed, the phase voltage instruction valuesV_(u), V_(v), and V_(w) are corrected by the correction unit 54 so thatthe interphase resistance differences are compensated (refer toEquations (20) to (22)), using the values of the phase resistancesR_(u), R_(v), and R_(w) obtained while the current sensors are normallyoperating. For this reason, according to the motor control devicerelated to this embodiment, generation of the torque ripple resultingfrom the interphase resistance difference is suppressed. Accordingly,even in a case where a current sensor fails, and the feedback controlcannot be performed, a favorable steering feel can be obtained.

8. Modification

Although only one current sensor 14 is provided in the above firstembodiment, a plurality of (two or three) may be provided. For example,in a case where current sensors for u-phase and v-phases are provided,the u-phase and v-phase current detection values used for thecalculation of the phase resistances R_(u), R_(v), and R_(w) in thephase resistance calculating unit 143 may use the u-phase currentdetection value I_(u) and v-phase current detection value I_(v) outputfrom the current sensors for u-phase and v-phase, and the w-phasecurrent detection value I_(w) may be obtained according to the followingequation in the phase current calculating unit 141.

I_(w)=−I_(u)−I_(v) In addition, in a case where a plurality of thecurrent sensors 14 is provided, the u-phase, v-phase, and w-phasecurrent detection values can be obtained at the same time. Thus, thestorage unit 142 is not necessarily required. In a case where threecurrent sensors 14 are provided, the phase current calculating unit 141becomes unnecessary (in a case where current sensors are provided by anumber equal to the number of phases). In this case, a current detectingmeans is constituted by the plurality of current sensors.

Additionally, in the first and second embodiments, the phase voltageinstruction values V_(u), V_(v), and V_(w) are corrected according toEquations (7) to (9) based on the phase resistances R_(u), R_(v), andR_(w). However, the invention is not limited to the correction by suchEquations (7) to (9). More generally, the respective phase voltageinstruction values V_(x) may be corrected so that portions equivalent toapplied voltages to the phase resistances R_(x) among the respectivephase voltage instruction values V_(x) have the positive relationshipwith the values of the resistances R_(x) in order to compensate theinterphase resistance differences (x=u, v, and w).

Meanwhile, when the angular velocity ω_(e) of the rotor of the brushlessmotor 1 is large, the counter-electromotive force becomes large, and theratios of applied voltages to the phase resistances R_(u), R_(v), andR_(w) become small. Thus, the influence of the calculation error of thecounter-electromotive force is easily received, and the calculationaccuracy of the phase resistances R_(u), R_(v), and R_(w) degrades.Accordingly, only when the angular velocity ω_(e) as to a thresholdvalue is provided, and only when the angular velocity ω_(e) is smallerthan the threshold value, the phase resistances R_(u), R_(v), and R_(w)may be calculated.

Additionally, the motor control device related to the first and secondembodiments is configured so as to drive the 3-phase brushless motor 1.However, the invention is not limited to this, and can also be appliedto a motor control device which drives a brushless motor of four or morephases.

Additionally, in the motor control device related to the secondembodiment, the feedback control and the open loop control are switchedto each other by the determination result in the failure monitoring unit34. However, the feedback control and the open loop control may beswitched to each other by determination (for example, by driver'sselection) other than determination in the failure monitoring unit 34.

In addition, the invention can be applied not only to the above-descriedcolumn assist type electric power steering device but also a pinionassist type or rack assist type electric power steering device.Additionally, the invention can also be applied to motor control devicesother than the electric power steering device.

9. Fifth Embodiment

Next, a motor control device related to a fifth embodiment of theinvention will be described with reference to FIGS. 13 to 16. The motorcontrol device related to the fifth embodiment, similarly to the aboveembodiment, is used for the electric power steering device shown inFIG. 1. Hence, description of the electric power steering is omittedherein.

FIG. 13 is a block diagram showing the configuration of the motorcontrol device related to this embodiment. The motor control deviceshown in FIG. 13 is configured using the ECU 10, and drives thebrushless motor 1 which has windings (not shown) of three phasesincluding u-phase, v-phase, and w-phase. The ECU 10 includes amicrocomputer (hereinafter abbreviated as a microcomputer) 20, a3-phase/PWM (Pulse Width Modulation) modulator 241, a motor drivecircuit 243, and a current sensor 245.

The steering torque T output from the torque sensor 3, the vehicle speedS output from the vehicle speed sensor 4, and the rotational position Poutput from the position detecting sensor 5 are input to the ECU 10. Themicrocomputer 20 functions as a control means which calculates a voltageinstruction value used for the driving of the brushless motor 1. Thefunctions of the microcomputer 20 will be described below in detail.

The 3-phase/PWM modulator 241, and the motor drive circuit 243 areconstituted by hardware (circuits), and function as a motor drivingmeans which drives the brushless motor 1, using the voltage of thevoltage instruction value obtained by the microcomputer 20. The3-phase/PWM modulator 241 creates three kinds of PWM signals (U, V, andW shown in FIG. 13) which have duty ratios according to 3-phase voltageinstruction values obtained by the microcomputer 20. The motor drivecircuit 243 is a PWM voltage type inverter circuit including sixMOS-FETs (Metal Oxide Semiconductor Field Effect Transistor) asswitching elements. The six MOS-FETs are controlled by three kinds ofPWM signals and negative signals thereof. That is, in the motor drivecircuit 243, two MOS-FETs are assigned to each phase, and the twoMOS-FETs are mutually connected in series to form a switching elementpair, and an inverter is constituted as such switching element pairs areconnected in parallel between a power supply terminal and a groundingterminal by the number of phases. Also, a connection point between thetwo MOS-FETs (switching element pair) corresponding to each phase isconnected to the brushless motor 1 as an output end of the phase in theinverter. The conduction state of the two MOS-FETs corresponding to eachphase is controlled by two PWM signals (two PWM signals which have aninversion relationship mutually) corresponding to the phase. Thereby,voltages obtained at u-phase, v-phase, and w-phase output ends N_(u),N_(v), and N_(w) are applied to the brushless motor 1 as a u-phasevoltage, a v-phase voltage, and a w-phase voltage, respectively. As thevoltages are applied to the brushless motor 1 in this way, the u-phasecurrent, v-phase current, and w-phase currents are supplied to thebrushless motor 1 from the motor drive circuit 243.

The current sensor 245 outputs detection signals showing the u-phasecurrent and v-phase current supplied to the brushless motor 1, and thesedetection signals are input to the microcomputer 20.

The microcomputer 20 executes programs stored in a memory (not shown)built in the ECU 10, thereby functioning as a q-axis current instructionvalue determining unit 221, a d-axis current instruction valuedetermining unit 222, subtracters 223 and 224, a q-axis current PIcontrol unit 231, a d-axis current PI control unit 232, a firstcoordinate transformation unit 233, a second coordinate transformationunit 234, a correction calculating unit 236, a correction storage unit237, a current detecting unit 214, and an angle calculating unit 215. Inaddition, the q-axis current instruction value determining unit 221, thed-axis current instruction value determining unit 222, the subtracters223 and 224, the q-axis current PI control unit 231, the d-axis currentPI control unit 232, the first and second coordinate transformation unit233 and 234, the current detecting unit 214, and the angle calculatingunit 215 constitute a control calculation means which obtains the phasevoltage instruction values V_(u), V_(v), and V_(w) showing phasevoltages to be applied to the brushless motor 1. Additionally, thecorrection calculating unit 236 includes three adders 236 _(u), 236_(v), and 236 _(w) corresponding to u, v, and w-phases of the brushlessmotor 1, respectively, and the correction storage unit 237 storesu-phase, v-phase, and w-phase correction maps 237 _(u), 237 _(v), and237 _(w). Such correction calculating unit 236 and correction storageunit 237 constitute a correction means which corrects the above phasevoltage instruction values V_(u), V_(v), and V_(w).

The microcomputer 20, as shown below, obtains the voltage instructionvalues V_(uc), V_(vc), and V_(wc) showing voltages to be given to themotor drive circuit 243, based on current instruction values showingelectric currents to be supplied to the brushless motor 1, and therotational angle (electric angle) of the rotor of the brushless motor 1.In addition, in the following, when description is made while payingattention to an arbitrary one phase of u-phase, v-phase, and w-phase,the phase to which attention is paid is referred to as an “x-phase” forconvenience.

The q-axis current instruction value determining unit 221 determines theq-axis current instruction value i_(q)* showing the q-axis component ofan electric current to be supplied to the brushless motor 1 based on thesteering torque T detected by the torque sensor 3, and the vehicle speedS detected by the vehicle speed sensor 4. The q-axis current instructionvalue i*_(q) is a current value corresponding to the torque to begenerated by the brushless motor 1, and is input to the subtracter 223.On the other hand, the d-axis current instruction value determining unit222 determines the d-axis current instruction value i_(d)* showing thed-axis component of an electric current to be supplied to the brushlessmotor 1. Since the d-axis component of an electric current which flowsinto the brushless motor 1 is not involved in torque, i_(d)*=0 istypically established. The d-axis current instruction value i_(d)* isinput to the subtracter 224.

The current detecting unit 214 outputs the detection values of theu-phase current and the v-phase current among electric currents suppliedto the brushless motor 1 from the motor drive circuit 243, as theu-phase current detection value I_(u) and the v-phase current detectionvalue I_(v), respectively, based on the detection signal from thecurrent sensor 245. The u-phase and v-phase current detection valuesI_(u) and I_(v) are given to the first coordinate transformation unit233. Additionally, the angle calculating unit 215 obtains the electricangle θ showing the rotational position of the rotor of the brushlessmotor 1 based on the rotational position P detected by the positiondetecting sensor 5. The electric angle θ is given to the first andsecond coordinate transformation units 233 and 234. In addition, when au-axis, a v-axis, and a w-axis are set for the brushless motor 1 asshown in FIG. 3, and a d-axis and a q-axis are set for the rotor 6 ofthe brushless motor 1, the angle formed by the u-axis and the d-axisbecomes the electric angle θ.

The first coordinate transformation unit 233 transforms the aboveu-phase and v-phase current detection values I_(u) and I_(v) into theq-axis and d-axis current detection values i_(q) and i_(d) which arevalues on the dq coordinate, according to the following Equations (34)and (35), using the electric angle θ.

i _(d)=√2×{I _(v)×sin θ−I _(u)×sin(θ−2π/3)}  (34)

i _(q)=√2×{I _(v)×cos θ−I _(u)×cos(θ−2π/3)}  (35)

The q-axis and d-axis current detection values i_(q) and i_(d) obtainedin this way are input to the subtracters 223 and 224, respectively.

The subtracter 223 calculates a q-axis current deviation (i*_(q)−i_(q))which is the deviation between the q-axis current instruction valuei*_(q) and the q-axis current detection value i_(q), and the q-axiscurrent PI control unit 231 calculates the q-axis voltage instructionvalue v_(q) by proportional integral control operation of the q-axiscurrent deviation (i*_(q)−i_(q)). The subtracter 224 calculates a d-axiscurrent deviation (i*_(d)−i_(d)) which is the deviation between thed-axis current instruction value i*_(d) and the d-axis current detectionvalue i_(d), and the d-axis current PI control unit 232 calculates thed-axis voltage instruction value v_(d) by proportional integral controloperation of the d-axis current deviation (i*_(d)−i_(d)). The q-axis andd-axis voltage instruction values v_(q) and v_(d) obtained in this wayare input to the second coordinate transformation unit 234.

The second coordinate transformation unit 234 transforms the aboveq-axis and d-axis voltage instruction values v_(q) and v_(d) into thephase voltage instruction values V_(u), V_(v), and V_(w) which arevalues on the 3-phase alternating-current coordinate (hereinafter, thephase voltage instruction values V_(u), V_(v), and V_(w) are alsoreferred to as a “u-phase voltage instruction value V_(u)”, a “v-phasevoltage instruction value V_(v)”, and a “w-phase voltage instructionvalue V_(w)”, respectively), according to the following Equations (36)to (38), using the electric angle θ.

V _(u)=√(⅔)×{v _(d)×cos θ−v _(q)×sin θ}  (36)

V _(v)=√(⅔)×{v _(d)×cos(θ−2π/3)−v _(q)×sin(θ−2π/3)}  (37)

V _(w) =−V _(u) −V _(v)  (38)

The phase voltage instruction values V_(u), V_(v), and V_(w) are givento the adders 236 _(u), 236 _(w), and 236 _(w) of the correctioncalculating unit 236, respectively, and are given to the u-phase,v-phase, and w-phase correction maps 237 _(u), 237 _(v), and 237 _(w)stored in the correction storage unit 37, respectively.

The x-phase correction map 237 _(x) (x=u, v, and w) is a map forcorrelating an x-phase voltage instruction value with the amount ofcorrection required for the voltage instruction value. The amount ofcorrection corresponding to an x-phase voltage instruction value V_(x)is obtained by the x-phase correction map 237 _(x), and the amount ofcorrection is given to an adder 236 _(x) corresponding to the x-phase inthe correction calculating unit 236, respectively (x=u, v, and w).

In the correction calculating unit 236, the adder 236 _(x) correspondingto the x-phase correct the x-phase voltage instruction value V_(x) byadding the amount of correction obtained by the x-phase correction map237 _(x) to the x-phase voltage instruction value V_(x) (x=u, v, and w).The u-phase v-phase and w-phase voltage instruction values V_(uc),V_(vc), and V_(wc) after correction obtained in this way are given tothe 3-phase/PWM modulator 241.

As mentioned earlier, the 3-phase/PWM modulator 241 creates three kindsof PWM signals U, V and W which have duty ratios according to the phasevoltage instruction values V_(uc), V_(vc), and V_(wc) after correction,and negative signals thereof. The motor drive circuit 243 is controlledby the three kinds of PWM signals and negative signals thereof, andthereby, the 3-phase driving currents (the u-phase current, the v-phasecurrent, and the w-phase current) are supplied to the brushless motor 1.Thereby, the brushless motor 1 is rotated to generate torque.

In addition, the current sensor 245 is inserted into u-phase and v-phasecurrent paths among current paths to the brushless motor 1 from themotor drive circuit 243, and the current sensor 245 outputs detectionsignals showing u-phase and v-phase currents supplied to the brushlessmotor 1 as mentioned earlier. Additionally, the rotational position P ofthe rotor of the brushless motor 1 is detected by the position detectingsensor 5 as mentioned earlier. The detection signals showing the u-phaseand v-phase currents, and the detection signal showing the rotationalposition P are input to the microcomputer 20, and are used for thedriving control of the brushless motor 1 as described above.

10. Regarding Correction of Phase Voltage Instruction Value

In order to suppress the ripple (torque ripple) included in the outputtorque of the brushless motor 1, it is preferable to form the circuitpattern of a motor driving circuit board (a circuit board on which themotor drive circuit 243 is mounted) so that an interphase resistancedifference is not caused in a motor/driving circuit system. However,even if the wiring pattern is formed so that a difference between phasesis not caused in resistance components of paths ranging from a powersupply terminal to a grounding terminal, a torque ripple is generated asto each phase if a difference is between the resistance component(hereinafter referred to as an “upper stage arm resistance”) of a pathfrom the power supply terminal to the output end of the motor drivecircuit 243, and the resistance component (hereinafter referred to as a“lower stage arm resistance”) of a path from the relevant output end tothe grounding terminal. On the other hand, when the wiring pattern isformed so that not only an interphase resistance difference is notcaused in the motor/driving circuit system, but also, the upper stagearm resistance and the lower stage arm resistance become equal to eachother as to each phase, the circuit pattern in the motor driving circuitboard becomes complicated, and the space for forming the circuit patternincreases.

Thus, in this embodiment, the difference (hereinafter referred to as an“upper and lower stage resistance difference”) caused between the upperstage arm resistance and the lower stage arm resistance as to each phaseis permitted in order to suppress an increase in the area of the motordriving circuit board. The phase voltage instruction values V_(u),V_(v), and V_(w) are corrected by a correction means including the abovecorrection calculating unit 236 and correction storage unit 237 so thatthe upper and lower stage resistance difference is compensated for eachphase in order to suppress generation of the torque ripple. Hereafter,the details of correction by the correction means will be described.

In this embodiment, the amounts of correction to be added to the phasevoltage instruction values V_(u), V_(v), and V_(w) in the correctioncalculating unit 236 in order to compensate upper and lower stageresistance differences are calculated with reference to a correction mapprepared for every phase. That is, the amounts of correction added tothe u-phase, v-phase and w-phase voltage instruction values V_(u),V_(v), and V_(w) are the amounts of correction correlated with theu-phase, v-phase and w-phase voltage instruction values V_(u), V_(v),and V_(w), respectively by the u-phase, v-phase, and w-phase correctionmaps 237 _(u), 237 _(v), and 237 _(w). Such u-phase, v-phase, andw-phase correction maps 237 _(u), 237 _(v), and 237 _(w) can be set sothat concrete handling methods of the phase voltage instruction valuesand the amounts of correction are different from each other. However,the methods of making or using the correction maps are the same in anycorrection maps. Thus, in the following, the u-phase, v-phase, andw-phase will be representatively described by the x-phase.

FIG. 14 is a circuit diagram for explaining making of the x-phasecorrection map 237 _(x) in this embodiment, and shows the circuitconfiguration of the motor/driving circuit system including the motordrive circuit 243 and the brushless motor 1. A resistance component froma power supply terminal N_(pw) to an x-phase output end N_(x), i.e., thex-phase upper stage arm resistance includes the ON resistance and wiringresistance of a switching element (FET) at the upper stage arm, and aresistance component from the x-phase output end N_(x) to a groundingterminal N_(gd), i.e., the x-phase lower stage arm resistance includesthe ON resistance and wiring resistance of a switching element (FET) atthe at the lower stage arm. In addition, although not shown in FIG. 15,a counter-electromotive force is generated in each phase of thebrushless motor 1 in a case where the brushless motor 1 is rotating.Hereinafter, the making of the x-phase correction map will be describedwith reference to FIG. 14 (x=u, v, and w).

In a circuit board (motor driving circuit board) on which the motordrive circuit 243 is mounted, even if a wiring pattern is formed so thatresistance components of paths ranging from the power supply terminalN_(pw) to the grounding terminal N_(gd) are equal to each other betweenphases, a voltage V_(xa) of the output end N_(x) deviates from anoriginal voltage when a difference (upper and lower stage resistancedifference) exists between the upper stage arm resistance and the lowerstage arm resistance as to the X-phase. In this embodiment, the amountof corrections of the x-phase voltage instruction value V_(x) forcompensating this voltage deviation is given by the x-phase correctionmap 237 _(x).

The voltage V_(xa) of the x-phase output end N_(x) of the motor drivecircuit 243 becomes

V _(xa) =D _(x) ·V _(b)  (39)

ideally (in the case of R_(b)=R_(g)=0) when the voltage of a directcurrent power source supplied to the motor drive circuit 243 is definedas V_(b), and the duty ratio which is the ratio of an “ON” period of aswitching element of the x-phase upper stage arm is defined as D_(x).However, practically, the upper stage arm resistance R_(b) and the lowerstage arm resistance R_(g) have values which are not zero, andR_(b)≠R_(g) is established. Thus, the voltage V_(xa) of the output enddeviates from a value D_(x)·V_(b) given by the above Equation (39).

Meanwhile, the x-phase voltage instruction value V_(x) output from (thesecond coordinate transformation unit 234 of) the control calculationmeans corresponds to an x-phase duty ratio D_(x) showing the ratio ofthe “ON” period of the switching element of the x-phase upper stage armof the motor drive circuit 243, and

D _(x) =V _(x) /V _(b)  (40)

is established. Since R_(b)≠R_(g) is established as described above,when two switching elements corresponding to the x-phase are driven atthe duty ratio D_(x) given by Equation (40), a voltage according to thephase voltage instruction value V_(x) is not obtained to the output endN_(x) of the motor drive circuit 243.

On the other hand, in this embodiment, the deviation of an actual outputend voltage V_(xa) to an ideal output end voltage V_(xa)(=D_(x)·V_(b)=V_(x)) corresponding to duty ratio D_(x) as to variouskinds of duty ratios D_(x) is obtained using the design values or actualmeasurements of the upper stage arm resistance R_(b) and the lower stagearm resistance R_(g) in each phase, and the resistance component(hereinafter referred to as a “motor phase resistance”) Rm of thebrushless motor 1. As to the various kinds of duty ratios D_(x), theamount of correction of the phase voltage instruction value V_(x)(=D_(x)·V_(b)) for compensating the above voltage deviation in the dutyratio D_(x) is determined, and is stored in the correction storage unit237 by using the data which correlates the amount of correction and thephase voltage instruction value V_(x) thereof or the duty ratio D_(x) asthe x-phase correction map 237 _(x) (x=u, v, and w).

In this embodiment, the phase voltage instruction value V_(uc), V_(vc),and V_(wc) after correction are obtained by adding the amounts ofcorrection obtained for every phase with reference to the u-phase,v-phase, and w-phase correction maps 237 _(u), 237 _(v), and 237 _(w)which are made in this way to the phase voltage instruction valuesV_(u), V_(v), and V_(w). According to the phase voltage instructionvalues V_(uc), V_(vc), and V_(wc) after correction, the respectiveswitching elements (FETs) of the motor drive circuit 243 serving as PWMvoltage type inverters are driven (ON/OFF). Thereby, the voltagesV_(ua), V_(va), and V_(wa) obtained by the output ends N_(u), N_(v), andN_(w) of the motor drive circuit 243 are applied to the brushless motor1.

11. Specific Example of Making of Correction Map

In order to make the respective phase correction maps 237 _(u), 237_(v), and 237 _(w) to be used in this embodiment, as to each phase, itis necessary to obtain how far the output end voltage V_(xa) (of themotor drive circuit 243) in various kinds of duty ratios D_(x) deviatesfrom an ideal value (=phase voltage instruction value V_(x)), using thedesign values or actual measurements of the upper stage arm resistanceR_(b), the lower stage arm resistance R_(g), and the motor phaseresistance R_(m). The voltage deviation at such an output end N_(x) canbe obtained by simulating the operation of a system including the motorcontrol device having the motor drive circuit 243 and the brushlessmotor 1 by a calculating machine, using the design values or actualmeasurements of the above resistance R_(b), R_(g), and R_(m).

An equivalent circuit showing a configuration for one phase in themotor/driving circuit system (FIG. 14) including the motor drive circuit243 and the brushless motor 1 is expressed based on a simple model,without performing such computer simulation, and the voltage deviationat the output end N_(x) can be obtained based on the equivalent circuitfor every phase. Hereinafter, a method of obtaining the voltagedeviation of the output end N_(x) in the x-phase by this simple model,and making the x-phase correction map 237 _(x) based on the voltagedeviation will be described (x=u, v, and w).

Both of FIGS. 15A and 15B are circuit diagrams showing the configurationfor the x-phase which is equivalent to one phase of the motor/drivingcircuit system shown in FIG. 14. In the simple model using this circuitconfiguration for one phase, the counter-electromotive force in thebrushless motor 1 is not taken into consideration. FIG. 15A shows a casewhere an x-phase current flows into the brushless motor 1 from the motordrive circuit 43, and FIG. 15B shows a case where the x-phase currentflows into the motor drive circuit 43 from the brushless motor 1.Additionally, in FIGS. 15A and 15B, a resistance component including theON resistance and wiring resistance of a switching element (hereinafterreferred to as an “upper stage switching element”) SWX_(u) at an upperstage arm is shown by an upper stage arm resistance R_(b), and aresistance component including the ON resistance and wiring resistanceof a switching element SWX_(d) (hereinafter referred to as a “lowerstage switching element”) at a lower stage arm is shown by a lower stagearm resistance R_(g). In addition, R_(m) shows the resistance componentof the x-phase in the brushless motor 1.

As shown in FIG. 15A, in a case where an x-phase current flows into thebrushless motor 1 from the motor drive circuit 243, when the upper stageswitching element SWXu is in an ON state, the x-phase current I_(x)thereof is

I _(x)=(V _(b) −V _(m))/(R _(b) +R _(m))  (41).

Thus, the voltage V_(xu) of the output end N_(x) at this time becomes

V _(xu)=(V _(b) −V _(m))R _(m)/(R _(b) +R _(m))+V _(m)  (42).

Here, V_(b) is the voltage of a direct current power source given to themotor drive circuit 243, and V_(m) is the voltage of a neutral pointN_(n) of the brushless motor 1. Additionally, since the brushless motor1 is an inductive load, in this case, even the upper stage switchingelement SWX_(u) is brought into an OFF state and the lower stageswitching element SWX_(d) is brought into an ON state, the current I_(x)shown in the above Equation (41) continues flowing. Accordingly, thevoltage V_(xd) of the output end N_(x) when the lower stage switchingelement SWX_(d) is in an ON state becomes

$\begin{matrix}\begin{matrix}{V_{xd} = {{- I_{x}} \cdot R_{g}}} \\{= {{- \left( {V_{b} - V_{m}} \right)}{R_{g}/{\left( {R_{b} + R_{m}} \right).}}}}\end{matrix} & (43)\end{matrix}$

Hence, the output end voltage V_(xa) equivalent to the x-phase voltageapplied to the brushless motor 1 can be expressed like the followingequations from Equations (42) and (43), using the duty ratio D_(x) whichis the ratio of the “ON” period of the upper stage switching elementSWX_(u).

$\begin{matrix}\begin{matrix}{V_{xa} = {{D_{x} \cdot V_{xu}} + {\left( {1 - D_{x}} \right) \cdot V_{xd}}}} \\{= {\left( {V_{b} - V_{m}} \right){\left\{ {{D_{x} \cdot \left( {R_{m} + R_{g}} \right)} - R_{g}} \right\}/}}} \\{{\left( {R_{b} + R_{m}} \right) + {D_{x} \cdot V_{m}}}}\end{matrix} & (44)\end{matrix}$

Meanwhile, an ideal x-phase voltage V_(xo) corresponding to the dutyratio D_(x), i.e., the voltage of the output end Nx when R_(b)=R_(g)=0,is

V _(xo) =D _(x) ·V _(b)  (45).

Additionally, the voltage deviation at the output end N_(x) isV_(xa)−V_(xo). Thus, in this embodiment, the amount of correction ΔV_(x)is set to

ΔV _(x) =V _(xo) −V _(xa)  (46).

Accordingly, when the design values or actual measurements of theresistance R_(b), R_(g), and R_(m) are given (V_(b) and V_(m) areknown), in a case where an x-phase current flows into the brushlessmotor 1 from the motor drive circuit 243, the amount of correctionΔV_(x) to the various duty ratios D_(x) can be calculated from Equations(44) to (46) in the case of D_(x)>0.5.

Meanwhile, as shown in FIG. 15B, in a case where an x-phase currentflows into the motor drive circuit 243 from the brushless motor 1, whenthe lower stage switching element SWX_(d) is in an ON state, the x-phasecurrent I_(x) thereof is

I _(x) =V _(m)/(R _(g) +R _(m))  (47).

Thus, the voltage V_(xd) of the output end N_(x) at this time becomes

V _(xd) =V _(m) ·R _(g)/(R _(g) +R _(m))  (48).

Additionally, since the brushless motor 1 is an inductive load, in thiscase, even the lower stage switching element SWX_(d) is brought into anOFF state and the upper stage switching element SWX_(u) is brought intoan ON state, the current I_(x) shown in the above Equation (47)continues flowing. Accordingly, the voltage Vxu of the output end N_(x)when the upper stage switching element SWX_(u) is in an ON state becomes

$\begin{matrix}\begin{matrix}{V_{xu} = {V_{b} - {I_{x} \cdot R_{b}}}} \\{= {V_{b} - {V_{m} \cdot {R_{b}/{\left( {R_{g} + R_{m}} \right).}}}}}\end{matrix} & (49)\end{matrix}$

Hence, the output end voltage V_(xa) equivalent to the x-phase voltageapplied to the brushless motor 1 can be expressed like the followingequations from Equations (48) and from (49), using the duty ratio D_(x)which is the ratio of the “ON” period of the upper stage switchingelement SWX_(u) at N_(x).

$\begin{matrix}\begin{matrix}{V_{xa} = {{D_{x} \cdot V_{xu}} + {\left( {1 - D_{x}} \right) \cdot V_{xd}}}} \\{= {V_{m} \cdot {\left\{ {R_{g} - {D_{x} \cdot \left( {R_{b} + R_{g}} \right)}} \right\}/}}} \\{{\left( {R_{g} + R_{m}} \right) + {D_{x} \cdot V_{b}}}}\end{matrix} & (50)\end{matrix}$

Meanwhile, an ideal x-phase voltage Vxo corresponding to the duty ratioD_(x), i.e., the voltage of the output end N_(x) when R_(b)=R_(g)=0, is

V _(xo) =D _(x) ·V _(b)  (51).

Accordingly, when the design values or actual measurements of theresistance R_(b), R_(g), and R_(m) are given, in a case where an x-phasecurrent flows into the motor drive circuit 243 from the brushless motor1, the amount of correction ΔV_(x) to the various duty ratios D_(x) canbe calculated from Equations (50), (51), and (46) in the case ofD_(x)<0.5.

Since the amount of correction ΔV_(x) to various duty ratios D_(x) canbe obtained from Equations (44) to (46) and Equations (50) to (51) asdescribed above, as to the phase, the x-phase correction map 37 _(x)which correlates the amount of correction ΔV_(x) with the duty ratioD_(x) as to the x-phase can be created (x=u, v, and w).

FIG. 16 is a view showing an example of a correction map made based onthe equivalent circuits of FIGS. 15A and 15B according to the abovesimple model. Here, FIG. 16 simultaneously shows the correspondencerelationship between the duty ratio D_(x) and the amount of correctionΔV_(x) for convenience regarding four cases including the case ofR_(b)>R_(g), the case of R_(b)=R_(g)≠0, the case of R_(b)<R_(g), and thecase (ideal case) of R_(b)=R_(g)=0. As described above, if the designvalues or actual measurements of the resistance R_(b), R_(g), and R_(m)regarding the motor drive circuit 243 of the motor control device whichis going to carry out the invention, and the brushless motor 1 are used(the supply voltage V_(b), and the neutral point voltage V_(m) areknown), the correction 2 map 37 x according to the resistance values ofthe resistances R_(b), R_(g), and R_(m) can be made as a correction mapwhich correlates the amount of correction V_(x) with the duty ratioD_(x) as to each phase. That is, the correction map 237 _(x) (x=u, v,and w) in which the upper and lower stage resistance difference and theinterphase resistance difference are reflected can be made. Thecorrection map 237 _(x) made in this way is a map which correlatesvarious duty ratios D_(x) with the amount of correction of the phasevoltage instruction value V_(x) by a curve (broken line) correspondingto any one of three cases excluding the ideal case (the case ofR_(g)=R_(b)=0) among the four cases shown in FIG. 16. Here, the dutyratio D_(x) can be expressed as D_(x)=V_(x)/V_(b), using the x-phasevoltage instruction value (before correction) V_(x). Accordingly, thex-phase correction map 237 _(x) can be used as a map which correlatesthe amount of correction ΔV_(x) with the x-phase voltage instructionvalue V_(x) (x=u, v, and w).

12. Effects

According to the embodiment, as described above, the phase voltageinstruction value V_(x) (x=u, v, and w) calculated by the controlcalculation means is corrected for every phase by the correctioncalculating unit 236 with reference to the correction map 237 _(x) madebased on design values or actual measurements, such as the upper stagearm resistance R_(b) and the lower stage arm resistance R_(g) (refer toFIG. 13), and each switching element (FET) of the motor drive circuit243 serving as a PWM voltage type inverter is driven (ON and OFF)according to the phase voltage instruction values V_(uc), V_(vc), andV_(wc) after correction. Thereby, even in a case where there is adifference (upper and lower stage resistance difference) between theupper stage arm resistance R_(b) and the lower stage arm resistanceR_(g) in the motor drive circuit 243, voltages according to the phasevoltage instruction values V_(u), V_(v), and V_(w) are applied to thebrushless motor 1 with high precision. Additionally, since the phasevoltage instruction values V_(u), V_(v), and V_(w) are corrected forevery phase according to the respective phase voltage instruction valuesV_(x) with reference to the correction maps 237 _(u), 237 _(v), and 237_(w) made for every phase, even in a case where an interphase resistancedifference exists in the motor/driving circuit system, an interphaseimbalance between the phase voltages V_(ua), V_(va), and V_(wa) appliedto the brushless motor 1 is suppressed.

Accordingly, according to such this embodiment, the torque ripple in thebrushless motor 1 can be reduced. Meanwhile, when an attempt to suppressgeneration of a torque ripple is made by forming a wiring pattern sothat the upper and lower stage resistance difference or interphaseresistance difference in the motor drive circuit 243 serving as aninverter is eliminated, an increase in the size of the motor drivingcircuit board is caused. On the other hand, according to thisembodiment, since the torque ripple is reduced by correction of thephase voltage instruction values V_(u), V_(v), and V_(w), an increase inthe size of the motor driving circuit board can be avoided, and anincrease in wiring resistance can also be avoided. For this reason, inthe electric power steering device using the motor control deviceaccording to this embodiment, an increase in the size of the motordriving circuit board is suppressed, so that the torque ripple can besuppressed to improve a steering feel while meeting the demand forminiaturization, low cost, high efficiency, etc.

13. Modification

In the above embodiment, there is provided a configuration (FIG. 13) inwhich the feedback control is performed so that the q-axis and d-axiscomponent of an electric current which flow into the brushless motor 1become equal to the q-axis and d-axis current instruction values i_(q)*and i_(d)*, respectively. However, the invention can be applied to acase where the brushless motor 1 is driven by the open loop controlbased on the circuit equation of the motor.

In addition, the invention can be applied not only to the above-descriedcolumn assist type electric power steering device but also a pinionassist type or rack assist type electric power steering device.Additionally, the invention can also be applied to motor control devicesother than the electric power steering device.

1: A motor control device for driving a brushless motor, the motorcontrol device comprising: a current detecting unit which detectsrespective phase currents which flow into the brushless motor; a controlcalculation unit which calculates instruction values showing respectivephase voltages to be applied to the brushless motor, and outputs theinstruction values as phase voltage instruction values; a phaseresistance calculation unit which calculates respective phase resistancevalues based on detection values of the respective phase currentsdetected by the current detecting unit, and the instruction values ofthe respective phase voltages applied to the brushless motor at the timeof the detection of the detection values; a correction unit whichcorrects the phase voltage instruction values according to therespective phase resistance values calculated by the phase resistancecalculation unit; and a driving unit which drives the brushless motorbased on the phase voltage instruction values after correction by thecorrection unit. 2: The motor control device according to claim 1,wherein the phase resistance calculation unit calculates respectivephase resistance values when the magnitude of the current which flowsinto the brushless motor is smaller than a predetermined value. 3: Themotor control device according to claim 1, further comprising a storageunit which stores the phase voltage instruction values after thecorrection when the respective phase currents are detected by thecurrent detecting unit, wherein the phase resistance calculation unitcalculates the respective phase resistance values based on the detectionvalues of the respective phase currents detected by the currentdetecting unit, and the phase voltage instruction values stored in thestorage unit. 4: The motor control device according to claim 3, whereinthe current detecting unit includes: a single current sensor whichdetects the electric current which flows through into the brushlessmotor; and a phase current calculation unit which calculates thedetection values of the respective phase currents sequentially, based onthe detection value of the electric current detected by the currentsensor, wherein the control calculation unit includes: anopen-loop-control unit which calculates the phase voltage instructionvalues according to the circuit equation of the brushless motor based onan instruction value showing an electric current to be supplied to thebrushless motor, and the angular velocity of the rotor of the brushlessmotor; and a parameter calculation unit which calculates the values ofthe parameters used when the phase voltage instruction values arecalculated according to the circuit equation, based on the detectionvalue of the electric current detected by the current sensor, andwherein the storage unit stores the phase voltage instruction valuesafter correction whenever the detection value of any phase current isobtained by the phase current calculation unit. 5: An electric powersteering device which gives steering assist power to a steeringmechanism of a vehicle by a brushless motor, the electric power steeringdevice comprising: the motor control device according to claim 1,wherein the motor control device drives the brushless motor which givessteering assist power to the steering mechanism. 6: A motor controldevice for driving a brushless motor, comprising: a control calculationunit which obtains instruction values showing respective phase voltagesto be applied to the brushless motor, and outputs the instruction valuesas phase voltage instruction values; a correction unit which correctsthe phase voltage instruction values; and a driving unit which drivesthe brushless motor based on the phase voltage instruction values aftercorrection by the correction unit, wherein the driving unit is adaptedsuch that switching element pairs including two switching elementsmutually connected in series are connected in parallel between a powersupply terminal and a grounding terminal by the number of phases, andincludes an inverter in which a connection point between the twoswitching elements corresponding to each phase is connected to thebrushless motor as an output end, and wherein the correction unitcorrects the phase voltage instruction values for every phase accordingto the phase voltage instruction values so that the deviation of avoltage at the output end caused by the difference between a resistancecomponent of a path from the power supply terminal to the output end ofthe inverter and a resistance component of a path from the output end tothe grounding terminal is compensated. 7: The motor control deviceaccording to claim 6, wherein the correction unit includes: a storageunit which stores a correction map showing the correspondencerelationship between the instruction values of phase voltages to beapplied to the brushless motor, and the amounts of correction for everyphase; and a correction operation unit which corrects the phase voltageinstruction values for every phase according to the amounts ofcorrection correlated with the phase voltage instruction values outputfrom the control calculation unit by the correction map, therebycalculating the phase voltage instruction values after correction. 8: Anelectric power steering device which gives steering assist power to asteering mechanism of a vehicle by a brushless motor, the electric powersteering device comprising: the motor control device according to claim6, wherein the motor control device drives the brushless motor whichgives steering assist power to the steering mechanism.
 9. An electricpower steering device which gives steering assist power to a steeringmechanism of a vehicle by a brushless motor, the electric power steeringdevice comprising: the motor control device according to claim 7,wherein the motor control device drives the brushless motor which givessteering assist power to the steering mechanism.